So my car won't start when it'* hot. I'm getting a trouble code for the throttle position sensor. So I changed, still having the same problem and code. The car shifts fine when driving, but won't down shift even with the pedal to the floor. I've checked the wiring and can't see anything. Checked my ECM, because it acts like it'* not getting any spark when it warms up. That was good. Please help!!

So my car won't start when it'* hot.

Pull your vac line off the fuel pressure regulator, and check for the presence of fuel....try starting with the MAF disconnected.......Do you have spark? Do you have good fuel pressure? Injector pulse?

I'm getting a trouble code for the throttle position sensor. So I changed, still having the same problem and code.

Did you check the signal voltage out of the TPS?....three wires, grey(5V), black(ground), and dkBlue is the signal voltage.....in the closed position, backprobe the dkblue wire, should be about 0.46V.....as you open the throttle it should increase linearly to about 4.7V.....if it doesn't, back probe the other wires checking for ground and 5V.....if ok, make sure the TPS is installed correctly and the linkage lever on the throttle plate is moving the lever on the sensor......

The car shifts fine when driving, but won't down shift even with the pedal to the floor. I've checked the wiring and can't see anything.

May not be getting a TPS signal to the PCM.....could be an open between TPS sensor and PCM.....

Checked my ECM, because it acts like it'* not getting any spark when it warms up.

How did you check your PCM?

I changed the fuel pump a little mor than a month ago. New fuel filter. Injectors cleaned.
I took my ignition control module down to get tested. It passed. Waiting for my friend with a tester to come over

And a new MAF about 2 months ago

A lot of the times an ICM will pass the that test, because when you take it in it has time to cool off, and it does not get heated up from all the heatsoak caused by engine operating temps, so just because it passed does not mean it is not faulting when the car heats up, considering all you have done, I cannot see much else that it could be, it is fairly common for the ICM'* to have issues with heatsoak if they are pretty old, at least from what I have heard, mine still works fine at 137k.

The next time you have the issue, I'd read this thread I am posting a link to, and test that ICM while it is hot, just be careful not to touch anything on the motor, I would not want you to get burned.

Part 1 -GM 3.8L Ignition Module Test and Crank Sensor Test (3X, 18X)