Generator Stalls only while Driving

Hi everyone! My first post. I bought a 1999 Safari Zanzibar and I am trying to solve a mystery. Auto transfer switch kept dropping the generator power so I bypassed the switch. Now, Onan 6500 propane genset purrs like a kitten while parked and running two rooftop ACs and the convection oven (total draw is 40 amps on both legs combined and 113 volts on each leg). However, the genset stalls when on the road. I noticed it occurred each time I came to a stop (three times I restarted it). After the third stop, I restarted it and turned on the front rooftop AC. The AC was rattling as if not getting enough power. I checked the genset and it was full throttle which is not normal for just one AC unit. Seems like a fuel problem to me. The propane fuel filter is not a replaceable type. It has to be rebuilt with new o-rings. Instead, I had sprayed carb cleaner into the air intake and put new sparkplugs. After that, it ran perfect parked. I wonder if liquid propane is sloshing in the tank when coming to a stop and not feeding fuel sufficiently??? The tank is 2/3 full. Since the governor had the throttle full open on the last test with one AC unit, seems it wasn't getting the fuel it needed. I'm sure it was not designed to allow a slosh problem but at 16 years old, it could be a malfunction in the delivery of fuel. I'm just not sure why it happens only while driving. I am out of ideas.:h