89 Corsica Engine Races When Shifting From Park

I have a 89 Corsica 4 cylinder 3-speed automatic transmission. When I go from Park to any other gear, the idle will dramatically increase and stay that way. I know this isn't good for the transmission. Also, it seems that the transmission stays in 1st gear way too long before shifting to 2nd. Once in 2nd or 3rd, if I press the accelerator too hard, it shifts back to 1st gear (downshifts). Anyone know what electronics controls the transmission shifting and/or idle? Could it be a bad ECM? Is there a modulator valve on these transmissions? I am almost positive that it is whatever controls the transmission, and not necessarily the transmission itself (fluid level is fine and fluid is not burnt). When it does shift, it has the nice smooth GM shift to it. Any ideas would be greatly appreciated. Thanks in advance!

I want to add, that if I drive down the road without my foot on the gas pedal, the car goes at a steady 35 MPH.

I would check to see if any trouble codes are stored in the computer memory to help. Sounds like possibly a TPS (throttle position sensor) which is pretty cheap, or possibly a bad vaccuum leak as well as a dirty /clogged IAC (Idle Air Control Valve). Of course, since it does this only when put into gear makes me think TPS. Would not hurt to check for loose/cracked hoses and clean IAC anyway. Don't know if transmission would cause this, but it does have a speed sensor in it. Try to get a trouble code if you can.

The only code I am getting from the check engine is code 44...lean exhaust. I am really suspecting its the ECM and going to replace that first, since I have access to that part rather easily. If that doesn't fix it, then I will certainly try your suggestions. I went over all the vacuum connections already and they all seem secure. I am leaning towards the computer more than anything because the engine idle AND the transmission shifting is not right. If it were just one problem, I would concentrate in that area. Can you tell me where the TPS sensor, as well as the IAC valve location? It is a 2.0 L TBI 4 cylinder. I certainly will let the board know my results. Thanks for your input!