I don’t know what type of controller this, but if it uses the old IBM wire contact relays (and the bigger Potter Brumfield), I’d start there in the leveling circuit and work back.
Sounds as if the generator isn’t the problem, because
The car lifts full load on inspect, but on auto, there’s a problem.

IBM= burnt pins, crossed pins, bent base pins and divots in the NO/NC sides, and failed coils.
PB= Broken shunt wires , worn contacts or contact fingers crooked and of course bad coils.

There’s probably more to this since the model is “Compu-“ whatever.
If there are slot boards…remove, look for obvious burnt components, clean the gold fingers, inspect the contacts where the board slides in if this the case, and reseat. If none of this applies, you’re no worse off than before. GL!

this is the controller with the horizontal selector above controller. dover composite

To see if you have a Generator problem, put a balanced load in the car, and tach the speed up, and down. The speed should be close to the same. If you are fast in the up by a lot you are under compounded.

Update: When running up the selector board is showing dz fail led. I can see that the 1sl and 2lr leds are both lit when in up leveling causing the issue. I have tried adjusting the emitter sensors on the up side but I’m maxed and it’s better but still doing it. I don’t think the distance apart is the issue since the down side sensors are close together and they aren’t causing issue. Unit has been down for couple years. We recently picked up the unit and trying to trace thru it. We don’t know what previous techs have done. I have an identical unit next to it, so I’ve been comparing the 2 but no luck.

Where are you located?

when it is stalled, what is your shunt field voltage and your motor field voltage. Sounds like you have a shuntfield resistor open inserting a large amount of resistance in the circuit. When is is trying to stall, jump from 2lr resistor tap to 1F resistor tap. I car jumps into or past the floor, your break is between Lev resistor tap and 1F resistor tap.