Put an external transmission cooler on and by passed the radiator. still have the same problem. Got my hands on a exhaust gas analyzer and it all checks out.

Greg, you say, in gear, wide open throttle (not turning the wheels) your max RPM is 1650.
MEngr asked (and it is my bet he was looking at the specs):
Is the engine's max full load speed at 2300-2600 RPM and the no load speed at 2800-3000 RPM?
your numbers are; "Rpm's at full throttle in netural are 3100 rpm's, [engine good] In reverse and forward with brake held at full throttle is 1650 rpm's".
[since it should be 2300 rpm, and you only see 1650, I stick with my wag that you need a torque converter].
Bite the bullet, pull the trans, change the trans soft parts (clutches, gaskets and seals) and a reconditioned torque converter.

Greg;
We are looking at an engine that may be down on max allowed governed speed under full load. The engine's full load hydraulic dead head (mast tilted back and held) to see engine's speed holds at full load governed speed. If it does, you have a stator problem in the Diakin 2 speed transmission. Check pressures of trans. with oil at normal temperature and engine's speed at 1000 RPM. The main pressure should be 145-185 psi, the FWR 1 will be 142-185 psi and the FWR 2 will be the same. Also, the REV should be at 142-185 psi. The converter (IN) pressure will be 43-85 psi.

Hydraulics are powered through the engine. Don't know if you have enough room to push the converter back or not, but thats a thought.

Not familiar with your exact model, but last thought- how hard is it to disconnect torque converter from flywheel? Would it be possible to push torque converter back so it's not rotating with engine (I understand your concern about burning up trans). Are the hydraulics powered through the engine or trans?

This is in nuetral and with the front tires off the ground in gear. Thought about looping the trans lines together temporarily to see if that would bring the engine temp down. Dont want to burn up trans. I have not ruled out trying that.

You said earlier that it takes longer for it to overheat at idle. Is this in gear or nuetral? Just a thought for a test- disconnecting the trans lines at the radiator & piping them together teporarily to see how the temp of the engine repsonds

I' ve thought about putting an external trans. cooler. But my opinon and my service manger are totally different, on that suggeston right now. Combustion test has been tested on coolant system and it was negative. Rpm's at full throttle in netural are 3100 rpm's, In reverse and forward with brake held at full throttle is 1650 rpm's.

I was discussing this situation with a collegue which had the same issue. Their solution was a custom oversized (3 row) radiator & they also installed an external trans cooler. They've been using the truck without issue ever since-

Hi Greg;
Having expierenced the issue from the time this series and model was introduced in 1997 to the last production in 2004. The timing you have set is correct for the fuel supply and engine family. Do you have the fan belt deflection set at 0.43 to 0.51? Are the plugs being used BPR4ES and gapped at 0.035? Is the distributor's air gap at 0.018? Is the engine's max full load speed at 2300-2600 RPM and the no load speed at 2800-3000 RPM? Is the full load fast idle control adjusted correctly and is it functioning correctly? Are the LPG components OEM UL rated as per factory bulletin of Apr 24,1998? With the air cleaner filter installed has the power adjustment been made properly? With Impco system is the secondary spring correct and is the air valve pressure for idle and full speed correct? Has the engine been checked for exhaust gases in the coolant?

just tell us how many RPMs you get at wide open throttle in neutral, then with the trucks brakes locked and in forward or reverse.

Exhaust system was replaced on this unit also, muffler had a hole in it blowing exhaust on radiator. while counterweight was off, radiator was blown out. Unit has been run without thermostat and the same problem exsist. Fan is on correctly and at the right angle. Temp is being checked with a mech. gauge. Unit has been drove without using the the paper roll clamp or the inching pedal. It does take longer for it to overheat at an idle. Timming is set at 8 degrees @ 700 rpm's. I have just about ruled out that this problem is comming from the engine. The transmission has only been serviced. I did find some rather large metal chewed up shims in the tranny strainer. I will have to get the pressure readings on the trans. I would like to at least rule out one of the two.

yep, edward has a good point
if the trans is heating up just as fast as the engine the heat transfer could be an issue if the tranny is the problem.
being they are connected together the heat could transfer through the tranny into the engine.....
though sometimes its hard to distinguish which one is the problem though. maybe you could get some heat indicator strips and stick one on each component to see which one starts showing indications of overheating while checking pressures

checking the tranny is a good idea so you can either find the problem or rule it out all together :o)

let me jump in with what I think this problem is.
does this unit "load up" when going up a hill or ramp, but idles well?
since you note the 230degree temp is in the transmission, also, and only after a less than 1 hour run, I think there is every reason to expect you have a bad torque converter (broken stator or stator blades).
Have you taken trans pressure readings and done a transmission stall test while watching the engine RPMs?

Have you verified the temp with an auxillary mechanical guage? I'd also check exhaust to see if it's plugged.