When you replace that pot you need to adjust it. 5 ohms right before the accelerator switch makes up. But I think your main problem is contactors. Remove the cover just behind the floorboard and check out the tips. You can try to drive the lift while looking and see where that buzzing is coming from that is usually from the drive motor getting some power but not enough to move. Their a lot of components behind the back panel but these usually will make the lift just not work or give very specific symptoms like trying to move and it jumps 1 or 2 times then cuts off. If the contactor tips are burnt all to crap (you will see the 2 that move one for forward travel another for reverse) Sometimes you can take them apart and use a file and lightly resurface the tips, keep in mind these need to make almost full contact to it's mate.
The tip should be a small dimple like mound if its just burnt to where their no dimple left the you would need a contactor kit to rebuild it. If you take this apart then mark cables and take pictures to ensure you put everything back in the right place.
That is just a EV operating system and fairly easy for experienced techs well us older people anyhow. I'm not sure what you call a lot of money one option would be to call and get a tech to look at it if you have no account it will be COD before he leaves meaning a call to the branch and a CC number. You could tell them you need a detailed quote from their and buy the parts yourself and replace them. Make sure to get with the tech and have him show you just what he found so you will know were the parts go.(could be as simple as a loose wire) For that operating system it should just cost the travel time to get their and no more than a hour to find the problem a good tech might find it quicker.
Or you can keep posting back and I will help all I can been working on them for 25 years but it's hard to go much further than the contactors without being their.
EDIT. On the contactor coil their 2 wires these are screwed to the coil on these old trucks make sure the wire is secure and tight, just unplug the battery before you try to remove anything or check for loose wires.