i have a 79 k5 350turbo tranny it is full time 4wheel drive but has a sticker that says a part time conversion kit has been installed my question is that after the tranny shifts into 3rd gear and i let off the gas the truck bogs down like it needs a 4th gear or someting i am running the t-case in neutral and the front hubs are unlocked but this still happens am i running the t-case in the right gear or is this truck just geared that low i have no idea what the gearing is

 

I doubt your problem has anything to do with the transfer case. You should be running it in HI range. HI-LOC should be used every once in awhile to engage the front output and lubricate the rest of the transfer case.

When you say it 'bogs down', does it just slow down rather quickly? How fast are you going when you let off the accelerator? How much does it slow down after a few seconds of coasting?