95 chevy van won't shift

I have a 95 chevy van with a 4l80E tranny. I have owned it for 3 years and have had no problems with it. During the summer I was gone for about a month and the van sat in the driveway. Upon returning I went to drive the van and it wouldn't shift at all. Then I noticed the speedometer wasn't really working either. It would move a little but very inacurate. Then I hit the brakes and the ABS light comes on and the wheels chattered. Long story short I have had it to 2 mechanics and one tranny shop with no results but the usual "It needs a rebuild". I tried replacing the speed sencors on the tranny but that didn't do anything. Then after reading about this problem on here a few months ago I replaced the ignition switch. It wasn't a instant cure but would begin to shift here and there, eventually after a few weeks began shifting fine again. The ABS and speedo problems stopped also.
Well, its been about 3 months and winter has hit. My battery wasn't handeling the cold starts so I bought a new one. After putting in the new battery.....here we go again. All three problems are back again. No shifting at all, speedo moves but is very inacurate, and the ABS also.
Obviously not just a ignition switch problem. Any help would be greatly appreciated. Thanks

Wewlcome to AF.
Check for codes Transmission and engine and ABS.
Clear codes and see what comes back.
Post back all code no.

You need to get the spedo problem fixed first.
No spedo no shift.

My '94 Astro acted about like that- whenever the "brake" fuse would blow- no speedo, no ABS and no shifting- traced it to a short in the ABS controller- I cut the hot wire to the controller- and never blew that fuse again. and never had the shift, no speedo problem again (they are all on the same fused circuit) You probably don't have a blown fuse, but you may be experiencing no power to this circuit- I would check the power at the "brake" fuse when you experience these symptoms- and then if no power- back trace it through the fuseable link- which is suspect. See if this fuse has power (ignition on) when you have the symptoms......

Also. is your van a "G" or "M" body?- and why is your post in the "C/K" forum?