I put this transmission in my car back in Oct. '07. It's a 4L60 out of a '91 L98 Z-28 with 78,000 miles on it. I've put 3,000 miles on the car since the install and have not had any trouble out of the tranny. It does'nt slip and shifts and downshifts when it's supposed to. With light to moderate acceleration you can feel the tranny shifting into each gear(normal positive shift), but with spirited or full throttle acceleration the tranny's shifts are softer and little sluggish. It's not slipping but the shifts are softer. Is this a sign that the transmission is getting ready to go south?

Anybody have any info.............???????

At what rpm at WOT are you shifting this?

How is your fluid level and quality? If I understood you correctly, that sounds very similar to what mine does when it gets a little low. Also, not sure if this would be related, but for optimal functionality your fluid should be red and relatively clean. If it's brown you might want to change sometime soon. As I understand it, the best way to meter your transmission's condition is to drain the fluid and see if there are lots of metal particles in it.

Im not a trans specialist but i would check the fluid level and smell/color,also the kickdown cable make sure it moves freely and it adjusted right. Other then that it sounds like normal wear to me with worn clutch springs.

The fluid is clean and red. It does'nt smell burned either. I changed the fluid, along with the front pump seal when I put it in the car. I did have to get a new dipstick tube grommet. The old grommet split while I was trying to put the tube back in the transmission. It didnt leak while the split grommet was in there though, but when I replaced it I lost some fluid. I thought I had topped it back off, but I checked the fluid yesterday and it was almost a pint low. There are no leaks, but it's possible that I did'nt put enough fluid back in.
As far as WOT shifts, it does'nt shift at WOT throttle. The best it does is shift at 3-3500 RPM. This tranny is a 4L60 out of 1991 Z-28 with L98 TPI 350.
I used my governor out of my original 700R4(4500 RPM WOT) vs. the governor from the Z-28(5000 RPM WOT). I adjusted my TV cable as per GM instructions and also Bowtie Overdrives. When I adjusted it the factory way, I had stacked short shifts, 2200 RPM WOT shifts, and no detent downshifts.
My TV cable was bad so I replaced it and readjusted. The part throttle shifts are dead on now,1-2@15-20mph,2-3@25-30mph, and 3-4@37-42mph. I also have my 3-2 and 2-1 detent shifts back. I dont have lock-up yet because the '91 lock-up wiring is different from my '86. I'm going to install a vacuum operated lock-up switch. As far as the 3-3500RPm WOT shifts, IDK.

Okay, I added a pint of fluid to my tranny, and now when I put my foot in it, it'll shift from 1-2 upshift, no problem, 2-3 upshift, soft,mushy shift....it doesn't slip, but it kinda goes uh....okay you want me go into 3rd gear now.....um alright I'll shift, 3-4 upshift,bussiness as usual, no problem. Other than the soft and mushy 2-3 upshift at WOT, the transmission does what it's supposed to do. It downshifts like it's supposed to, and there are no mushy shifts with normal accelleration. Should I do another drain and fill and see if that fixes the problem? Is my 3-4 clutch pack getting ready to crap out? And where should the fluid come up to on the dipstick when its' full? I only paid $100.00 for this tranny and so far I've gotten roughly 3100 miles out of it since I put it in my car. If it's getting ready to call it quits, no problem,I just want to know so I don't kill it completly.

Okay, I added a pint of fluid to my tranny, and now when I put my foot in it, it'll shift from 1-2 upshift, no problem, 2-3 upshift, soft,mushy shift....it doesn't slip, but it kinda goes uh....okay you want me go into 3rd gear now.....um alright I'll shift, 3-4 upshift,bussiness as usual, no problem. Other than the soft and mushy 2-3 upshift at WOT, the transmission does what it's supposed to do. It downshifts like it's supposed to, and there are no mushy shifts with normal accelleration. Should I do another drain and fill and see if that fixes the problem? Is my 3-4 clutch pack getting ready to crap out? And where should the fluid come up to on the dipstick when its' full? I only paid $100.00 for this tranny and so far I've gotten roughly 3100 miles out of it since I put it in my car. If it's getting ready to call it quits, no problem,I just want to know so I don't kill it completly.