shift problem

ok hears the deal....i have an 84 z28 with the l69 and 700r4 trans.. the problem comes when i stomp on it, it goes fine until it hits redline in 3rd, after that it wont shift into fourth unless i let off the gas. then if i step back on the gas it downshifts and sits at redine i really would like to find out what the car can do but this is kinda limiting me. any help you guys could offer would be very helpful

natural, it's the kickdown valve in the 700R4.

Could have worn O-rings, but the action is natural, it won't
shift at WOT without a special kickdown kit that'll allow it to.

any idea where i can get such a kit or the cost of it?

Jeg's offers them for around $30.
TH-700R4 Kickdown Kit #130-70237

Don't quote me on this, BUT

If third and fourth gears are slipping, then the 3-4 clutches are burnt (see how that works...) Third and fourth gear share a set of clutches called the "3-4 clutch pack assembly" and is a very common problem w/ the 700R-4. The only way to fix is to remove the transmission and overhaul. While your in there, don't just replace the clutches like most shops would do, try to actually fix the problem by air testing the input housing and look for leaks around the input shaft, check or just flat out replace the 3rd clutch capsule, and install a transgo reprogramming kit. I've seen properly built 700's go 200,000 miles or more, and I have seen not so well built trannys burn those clutches up at 20,000 miles (from the factory) and 5,000 miles from podunk local shops

I got that off another website, this may be your problem.....

the trans dosent slip...it just dosent want to shift into 4th at WOT

You could block the 4-3 part throttle downshift holes in the TV plunger sleeve with two very small allen screws. There some pictures about this somewhere on this site or third gen.org in the past several weeks on how to do this. In the future, I will put this modification (how to) on my website. This will allow 3-4 WOT shifts.