Old thread, I know. But just to follow up on this, I am an EFI tuner and Lew is right. The transmission shift points and torque converter lockup points can be altered with a chip.

On these older transmissions, it's a bit of a guessing game anyway. You tell the PCM what RPM to shift at (at WOT), and that's when the shift BEGINS, not ends. Meanwhile, the engine is rapidly accelerating. So by the time the shift is complete, the RPM is higher than when we command the trans to shift. For example, I command a 4800 RPM 1>2 shift, and it completes at 5600 RPM maybe. But first gear accelerates in RPM faster than other gears, because it's a lower gear.

In 2nd gear, I might have to command 5400 to get it to shift at 5600, because engine RPM doesn't accelerate as fast in 2nd as it did in first. Same with 3rd gear, and so on.

Also, WOT shift RPM is different than part throttle, where the MPH becomes the primary shift input. So while at WOT the RPM may dictate the shift and be consistent, if you have a problem with the accuracy of your output shaft sensor, the MPH input may not be correct and the part throttle shift MPH may not be right.

So much of this went away with newer Fords, where the gear ratio and tire size were programmable in the PCM. On those, there is a Vehicle ID block, where a good scantool can enter in the gear ratio and tire size, but with limitations on how far you can increase or decrease either.

With a chip or programmer and custom tuning software, I can enter in just about any gear ratio and tire size on those, without much of a limitation. We can go a lot further than the dealer can, because they can only access the Vehicle ID block. In the tune, I can access those limitations and more.

Of course, a chip can do a lot more than just this. For example, I can change the firing order from the older 302 order to the newer 302HO/351W firing order. And anything else I want. Of course, there's also all the performance stuff too! :-)

Steve @ Drag Radial Performance