TH350 reverse and second only

[werewolfx13]

This transmission has me pulling my hair out.
First few drives with my freshly rebuilt TH350 in my '76 k20 went fine, truck now only has reverse and second gear. Takes off in second, try to manually downshift into low and the engine feels like its in gear, and if you goose it a little, it'll creep forward, but feels like its hooked to a tree, downshifting into first while moving doesn't seem to force a downshift, but rather just makes it feel like the truck gained an extra 10,000 lbs, shift back into drive and the "pull" is gone. Reverse works great, and second works great. Will not upshift into third at any rpm, with or without the detent cable connected at the carb. Modulator is new and has vacuum.
Only modification that went into the trans during the rebuild was a transgo 350 - 1&2 reprogramming kit. Drawing a blank on what governor springs I installed, but per the transgo instructions, they were for the latest shifts as recommended for heavy use 4x4 vehicles. The modulator valve spring was also left out per instruction for hardest/latest shift.

I honestly can't physically wrestle the transfer case back out of the truck again, and can't really afford to pay a guy to help me get it out and back in again. I'm REALLY hoping this is a simple linkage/valve body problem. Any thoughts before I drop the pan again?

[Fairlane514]

Sounds like you may have some trash in the valve body.  Pulling the valve body isnt too bad, you could go through each valve one at a time and clean them. They should move freely in their bore. Use a small pencil style magnet and run them up and down in the bore with some brake clean.

[werewolfx13]

I'll drop it back out and clean it out again. I cleaned it when I installed the transgo kit, but I suppose something might have worked its way into it. Thanks.

[hydrospec2001]

I had a problem with my TH350 about two months ago. Not sure if it will help but my governor had gone out. There is a small nylon gear at the end of it and it unexpectedly was smashed. The difference is I only had first and reverse. It's very easy to check though without dropping the pan. It's under the dome shaped cap on the side of the transmission. It will leak a little bit of fluid. Maybe a half quart or so but the governor should pull out really easy.  Not sure if this will help but if it fixes the problem at least you don't have to drop the pan again.

[werewolfx13]

The governor is good, its accessible through the removable tunnel, so its the first thing I checked on. When I rebuilt it, the governor gear was in the best condition I've ever seen on a used trans.

[74 C-10 Shorty]

First thing check linkage all the way to the shift valve in the valve body, could be dirt also could be a valve in the kit put in backwards or a spring in wrong location very easy to do, might want to double check that.