It never ends! After mastering the art of 3rd gen p-brake, changing cam and heads, lowering the front (several attempts to get it right, like 5) now the time has come to the tranny.

Yesterday, on the highway, I lost 3 and OD on my 4L60. It acted just as if I was in N. Didn't slip or anything - it was just gone and did absolutely nothing to pull the car forward.

My tv-cable is set to the bottom (max to the firewall), making it shift as late as possible. It's tight at WOT.

I have felt no slipping at all in 3rd and OD. Historically it has flared a little bit when going from 2 to 3 to OD but then I have let go of the throttle. The car has seen 99.9% cruising.

A couple of weeks ago I changed oil and filter. The old oil smelled a little and there was some gunk in the bottom of the pan, but not much. I put in mobil1 synthetic atf.
Could the new synth atf have cleaned the inside and make something stick or did the clutches just give up without notice?

(Car is a Trans Am -91 with about 70k on the meter)

What is my next step? Crawl up into a ball and pay for a complete rebuild?

 

Sounds like it needs a rebuild. The flared 2-3 shift was the indicator that it was getting ready to let go. My 7004R did the same thing a long time ago. It started the flared 2-3 shift a few days before it lost 3rd and 4th. After that, it would work fine in 1st and 2nd, but then the shift to 3rd would be like shifting to neutral. I had to drive in 2nd gear for a few days until I could get it into the transmission shop. Full rebuild and it was good to go.

The transmission had about 110K on it at the time. It failed about 3-4K miles after I changed the transmission fluid.

 

Mine has flared a little for three years, since I got the car. Well, I think Im gonna add a sub-harness to my Fitech ecm and run a 4L60E instead. I don't like that tv-cable. The 4L60E in my trailblazer has 150k on it and doesn't miss a beat.