Did you ever check if all the bolts are in the calipers? One fell out on my sisters car. The caliper would swing out against the rim and lock it up, In reverse the caliper would drop back in place. I drove 20 miles in reverse to get it home, LOL

 

I did check the calipers and they look good.

 

I may have missed it as I scanned the 7 pages quickly, but have you taken the front drive shaft off and driven it? If it still does it you know it's not the transfer case but in the front axle.

I was also thinking a locking front brake causing the lugging until put in neutral. Do you have 4-wheel ABS? Could be the sensor, or the proportioning valve (aluminum block with lines by the fuse box).

 

I'd take the front cover, the CAD, and the hubs apart and completely inspect the front axle. I'd take the rear brake drums off and have a look also.

 

So I've been really running every single vacuum line on the truck and I found something suspicious. The connection to the solenoid right next to the shift linkage on the transmission has about 6 wires coming in and every single wire is completely bare and twisted together. They are nearly welded together. I think this may be the jumping problem. Gonna hit up a junk yard this weekend and get that replaced.

 

I put some heat shrink over all the bare wire. It stopped the jumping. But it still has absolutely no power. It wouldnt even pull itself up a hill. It's fine in reverse. And it won't shift down from drive when you stop. So I have to gear it down manually. I guess I will get a new solenoid. Will that make it have no power?

 

Lets back up to your 1st post, you need to pull the front diff cover immediately, what your describing hear is a ring and pinion that's locking up!! leaving only the differential to operate, this would explain why one wheel starts to rotate backwards while driving down the road..

 

What am I looking for in the differential? Also, when I first got the truck I change the front differential seal and when I did, there was less than half of a quart of oil in it.

 

That's not a good sign.....

If you turn one wheel, and the other wheel spin in ANY direction, that indicates that the cad is not doing its job...... Need to find out why.

 

When I mentioned the wheel spinning, I was talking about the rear axle. The front does not do that. I think the CAD is working properly