no power going up inclines

[jim@nuggetrvpark.com]

I have a 1988 36v DS cart that struggles to climb even a slight incline. Acceleration is normal and speeds are fine on level ground. Last year it developed the "herky jerky" acceleration from a start so I replaced all five of the solenoids which corrected that problem immediately. It did have the low power problem at that time but nowhere near as pronounced as it is now.
Batteries and connections are OK, they are older trojans but they all read over 6 volts when disconnected and around 38 when hooked up. I have a small hand-held load tester and I load tested each battery while they were disconnected.
Here's my problem... This cart serial number is A8831 which from what I have learned so far is that it should have the V Glide switch which could be a suspect.... Nope, it has the electric speed switch which is found on 80-87 models. I have no idea what the history of this cart is but everything is stock.
I suspect the speed switch but having no experience with testing it I'm debating if I should throw more money into this old relic or start looking for a newer cart.
I have a fluke multimeter and I know how to use it if anyone has any information.
Thanks for any advice!