This may be long, but I appreciate any advice.

Anyway, my tranny has not been shifting at 75% throttle to WOT. But if I give it just enough gas to get to redline or close to it, it will shift like normal.

Sounds like a slipping tranny, but the *weird* part is, when I give it lots of gas I get to around 4k rpm it seems like it just comes out of gear and starts free-revving.

Fire away if you can guys....

 

Yeah, sorry to tell you this but it definitly sounds like it is on it's way out.. To explain your "weird" thing, there is a pump slide spring, in you pump obviously, and they are known to be a little weak from the factory..
It sounds like your is getting weak and causing the free reving at that low of an RPM, free reving isn't good because that means your clutches are going to be or already are worn down..

There are many flaws with the design of the 4l60e, and just an FYI if you take it to a shop make sure they know how to over come those factory flaws..

The good thing is there are many good builders on this board, and one of the best... See the tranny in my sig for more details, or search for CPT in this section..

Good luck with it.

 

Thanks