Just returned from a 700 mile round trip in my 80 300d, car ran fine, except on the way back. On the highway going 70mph, when approaching a hill or having to give it more gas, it acted like it was not getting fuel or cutting out. Once I let off accelerator it was fine.

The car has new fuel filters less than 4K miles ago or back in August. Engine temp ranged from 90 to 100C, A/C on. 165K miles on the car, maintenance is up to date. I have noticed that the car seem to run rougher than normal with the A/C on and stopped in gear. I thought perhaps it was running low on fuel, sometimes I don't trust the fuel gauge. Filled it up with almost 12 gallons, but the problem continued. Is there a shutoff if the engine RPM get's top high? Any thoughts?
Thanks