after this weekend my car only has reverse, 1st and 2nd.
No 3rd or 4th. Have 18,563 on the car but she gave up the ghost.

Have a Yank3000 and have been Spraying thru shifts. Before cam, headers, exhaust car dyno'd at 456tq so think the extra power and tq are what did mine in.

Anyone else have this problem......and how did you fix itand make it bullet proof?

 

I have the same problem, lost 3rd and 4th. I haven't fixed it yet. I just got tired of dumping money into the car.

 

You need to increase the volume going to the clutches if you want them to hold up under heavy loaded shifts. A better set of 3-4 cluthes are also in order, as well as line pressure modifications.

 

When the TC was installed my buddy increased the line presure slightly with HP tuners software. Right now I am looking at getting another 4l60e that is in the same condition as mine and having it rebuilt. It has the corvette servo and a few other upgrades all ready but needs the 3-4 clutches and sprag replaced. Think it might be cheaper to just have it rebuilt.

I have heard the clutch and sprag are the "Achiles Heal" of the 4l60e

 

3-4 clutches are the #1 failure. Sunshells are probably #2. Sprags don't happen as frequently, but they do go bad, and there is better out there.

Tuning can increase part throttle pressure, but can't change the actual max. If you take a stock program, and go WOT, you'll notice the PC Solenoid is at 0.10 Amp, which is the max, so you already get the max at WOT, even with a stock tune. The line pressure max is a hydraulic function of the transmission itself, so you need boost valve/valvebody modifications to get the max higher.