Another thing occurred to me just now. Having recently immersed myself in the 700r4 / 4l60 / 4l60e for the purpose of building / rebuilding the transmission in my wife's daily driver, I learned one particular tidbit that makes me want to caution you about excessive RPM or torque in first gear.Originally Posted by kur4o
This transmission's primary weak point is the 3rd gear clutch and the fact that the check ball for the 3rd gear apply tapering tends to wear the valve body separator plate until it sticks itself into the hole and causes timing problems that make the 2-4 band eat the 3rd clutch pack with 4-3 shifts under power. You can change your trans fluid and filter every two weeks and still have this eat a high-mileage transmission.
The second biggest point of weakness, and the one you want to pay attention to with high RPM and / or torque is the sunshell that keys itself into the 2-4 drum. In first gear this very large and heavy assembly rotates at double crankshaft rpm (not accounting for torque converter loss). Without a beefier sunshell and / or 2-4 drum, the interlocking fingers can bend under the extreme centrifugal force to the point they cut into the transmission case. Similarly, healthy increases in torque can also fracture the splined drive collar completely off the sunshell, or strip it's splines off.
If you aren't big on learning how to rebuild an automatic transmission I would encourage you to tread lightly, particularly if you have sticky tires and modified shift pressures.
These transmissions can be built to withstand serious abuse with a hardened sunshell, 2-4 drum, and beefed up 3rd gear clutch pack. But I wouldn't spin the factory components past 10,000 RPM (5,000 at the crank / input shaft) under heavy torque conditions, particularly if they have a lot of miles on them.
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