I have an 86 K10 with a 700R4 and 3.42 rear end with 29.5" tall tires. Coupled with a 305. It's a dog. struggles to get to 65 on a good day. Bucking the wind, forget about speed. Pulling hills sucks as well. So I would definitely stick with the 3.73.
Also, there is a fusible link around the steering column on the engine side of the firewall. Check that as well. Had one blow there when I hooked the battery up backwards. Same symptoms as you describe.
Go around the whole vehicle and clean every ground wire you can find. Several by the emergency brake pedal, several on the core support, passenger side engine head to body, battery to frame to name a few.
You might try contacting @Grit dog, he's up in the Pacific northwest. Apparently there are a lot of squares up there so maybe he could fix you up with some info.
Oh, I thought you meant you were going to start wearing a pocket protector along with a pocket calculator!! :anitoof: My son has been toying around with building his own electric using a 63 Impala as his base. He's already built himself an electric go-cart. Also has a company building the bit...