I have not done anything with the regulator. It runs fine on LP so I did nothing with that side of it. I will try checking the distributor this week and let you know.

my first choice would be to hook up a timing light with the vac line on the distrib to see it advance as you accelerate, next choice is to take distributor cap off, if vac operated, draw a vac on the line to see the plate move.
have you cleaned/drained the "honey" from the regulator?

I have also noticed that the problem is not as bad when it gets warmed up.

I was wondering about the vac advance. What is the best way to check if it is working properly?

set timing? checked to see the vac advance in distrib is working and connected properly?

Until computer controlled engine timing* came along to forklifts, most forklift mechanics "in the know" considered "dual fuel" to be a cruel joke on forklift mechanics, since we knew that in order to get a conversion from LPG to Gasoline (or the other way around) to run correctly required a change in the ignition timing by about 5 degrees, and we usually "split the difference" with a slight advantage to whatever fuel system was most likely to be used.
if your truck is "pre-emissions controls" be sure that you run all the fuel out of 1 system before you try the other system, or you may have too much fuel in the combustion chamber, which can sometimes cause symptoms somewhat like you describe.
*Computer controlled emission dual fuel trucks have 2 sets of computerized settings, 1 for LPG and 1 for gasoline, so the dual fuel actually works correctly, but the computer learning process requires 2 sets of "learn", 1 for each fuel source.

I know for fact the accelerator pump is working, can see the fuel being shot into the carb after I cleaned it. I am not real great with carbs, thought I had everything real clean. Not sure I know what the pilot circuit is. Runs great wide open once I get the RPM's worked up. Do I have to pull the carb back off to know if the pilot circuit is working? Any other suggestions?

I would guess the carburetor pilot circuit and/or accelerator pump still has problems.