I'm sorry but i have no info on your model.
Was looking for the electrical plan to see what sensors are fitted..

Model h45d-600
Serial/year h2x352k0268345/1999
Diesel with a Perkins 6000 hours

Whats the serial number?
Looking for the buildnumber like H2x...

When i first start it in the morning the foot pedals activate the throttling up and down just fine. And when it seems to begin either building pressure in the system or if it is the oil getting hot. That's when the throttle begins to fade and not want to throttle up at all. That's when I have to start running the forks up or run the tilt to make it start throttling up for it to go. And as it begins going forward or rev it is gutless.
I then can gain some of the throttle and torque back by running a water hose for about a min over hyd system/components and then it works fine for a bit.

When the problem occurs, does engine rpm go up when lifting or tilting?* edit, it does. sorry.
What's the trucktype? Like BR393, BR394...
Had the same symptoms with a LPG powered model > broken intake air temp.sensor, resulted in no fault codes. All temp.sensors are monitored by the ecu resulting in fault codes. With the dedicated diagnosis tools you should be able to able to find where the fault occurs.. it also helps to have a mechanic that knows how these trucks have to behave, react and sound.. Like duodeluxe states... don't fool around with hydrostatic units..

I didn't mean to offend anyone. It just gets old knowing every time a certain expensive piece of equipment that breaks down on me. If taken to the local dealer I already know the outcome of there diagnosis. It's all about Replace multiple high dollar parts and then being told like they turn into salesman how much more cost effective it is to buy new. Almost compared to dealing with a Medical Doctor. Go in there for a physical feeling just fine but leave the place with 5 prescriptions , told blood pressure is high, high Cholesterol , and the mole on my chest looks weird and they want to cut it off. It's all about the up sell and money to a lot of these big outfits. Where I'm getting at is whatever happened to the shade tree mechanics who used to give tricks of the trade that aren't in the repair books.? Whatever happened to helping someone else out that obviously isn't an expert in the field that he is asking about?

"They have no clue period on how to trouble shoot. They are just part replacers who bank on eventually it being the right part that needed to be replaced."
You just described a lot of dealer mechanics. Big Red and Ugly beige are getting so many national contracts, they need lots of mechanics to service their growing fleets. They sell trucks at cost, to brag about being #1. They have subsidized labor, big contracts and retain mechanics even if they have no work for them. 2 techs that worked with me got jobs at red and beige, make 7$ per hour more than me, but could not diagnose the cord on a toaster. Call an independent forklift tech.

Rich block? What is that ? What does that part do? It could be just something simple like that. And not something serious like a pump or a motor

The local dealer sucks. They have no clue period on how to trouble shoot. They are just part replacers who bank on eventually it being the right part that needed to be replaced. The symptoms being shown that are occurring doesn't tell me that the parts are broken. It tells me that as parts tend to wear certain components need to be adjusted. Pressure relief valves or whatever. It's always easy to just send it to the dealer and let them gouge me or let them talk me into buying another one. I thought I'd try asking a forum a question and maybe some other poor boy like me had something similar happen to them and they could lead me in the direction they took.

Stop experimenting and call a your local Linde dealer.

I would change the rich block under the pedal

I tried the correct fluid and it did the same. I also tried a little heavier f oil and it did the same. I will check the shaft to make sure it's turning. And I have changed the spin on filter and the filter in the tank as well with genuine linde filters. I'm almost thinking it has something to do with pressure being built up In the system and it's causing the fluid either not bypass enough or bypass to soon or to late. Because I can lift the mast all the way up and then I will shut the engine off. While dropping the mast down until it hits the ground , you can hear air leaving the vent at the oil fill cap. I know it's doing it's purpose by releasing air out of the system but it seems like it's a lot.
I agree with you linde made a great machine and when it's working correctly I don't think it can be beaten. That's why I believe It's got to be something minor needing to be adjusted or something. Cause it works great for a bit until it gets warm, or until it builds pressure

The engine must accelerate when you step either the forward or reverse pedal. It must also accelerate correctly in conjunction with the the operation of the hydrostatic pump.
With the engine OFF remove the floorboard you will see the linkage that goes from the F/R pedals connected to a small splined shaft that goes into the " black box". Make sure the shaft is turning when you press on either pedal.
What hydraulic fluid did you use? You MUST use ISO 46. Most auto parts only sell ISO 32.
Did you change the hydro drive filter? It is located behind a sheet metal door behind the mast. Only use a Linde filter which is a high pressure filter. If you use an aftermarket one then it could blow apart.
This is a bullet proof truck. one of Linde's finest.

I bought from a forklift company used. I bought it in the winter and had no problems with it in the winter. The engine accelerates just fine using the lift valve and tilt valve. But not the foot pedals. I checked the temp at different areas like tank, hoses , pump , control valve, check valves cylinders, return hoses, filter, actuator with one of those temp laser readers. And it only got up to 146 degrees at the control valve but most everything else I checked was around 139 to 144 degrees. So it isn't to hot to start damaging pumps or motors yet.

Have you had this truck for a while or did you just acquire it? If you just got it where did it come from?
When it is hot does the engine accelerate properly but the truck hardly moves?