trader0397

I have a 71 Chevy C-10 with a 98 Camaro LS1 engine and a 4L60E trans. I bought this last fall and was told that it had 1200 miles on it since the motor and trans were put in the truck. Since day one, when I got it, the transmission has not shifted right. If you drive normal, it will shift fine from 1-2, from 2-3 it is like it goes to shift, but hesitates and alows the motor to rev then shifts (firmly). Sometimes, with your foot in it, it will do this from 1-2nd also. At cruise speed, if you kick it down, it shifts fine. Not sure what or who tuned this, but could it be the tune? or, could it possibly have some kind of shift kit making it do this? My thought is that it is the tune, but not sure. Fluid looks good and is proper fill.

pricesgarage

need to put a line psi gauge on it before you do anything

mrvedit

A 2-3 flare is generally either due to a leak in the 3rd apply circuit, a worn out 3-4 clutch, low line pressure, or a combination of those.
A 1-2 flare is relatively rare and having both flares indicates a line pressure problem, as pricesgarage implied, or a seal problem on the 2nd apply piston on the servo.

Take the car to a trans shop and have them check the line pressure. Generally it will be about 50psi at idle in Park/Neutral and quickly rising to 175psi (or so) when you blip the throttle. It will also be 90-150psi in Reverse. If a shift kit or bigger boost valve were installed, it will be higher. Best is to monitor the pressure during WOT shifts.
Alternatively, buy a trans pressure gauge on ebay for $45 and check it yourself.

And yes, the tune controls the line pressure.