Newbie having some trouble with '99 Alero

[cts24]

I'm having some trouble with my 1999 Alero.... I hear a buzzing sound when the auto. trans. is shifting from 1st to 2nd and 2nd to 3rd.... when I get up to about 50 - 55 and keep at a constant speed, it stops. The best way I can describe the sound is a baseball card in bicycle spokes, just faster.
Also, I can feel a slight miss when running at about 40 - 45 mph. It feels like I've lost some of the power it once had, especially going up hills and I really have to punch it when going up steep grades. It feels like I'm driving into a heavy wind coming at me... like its holding the car back. I've read of people having a similar problem... they changed plugs, wires, fuel filters, etc. but still had it. Then they found out the pcm or ecm was going bad.
Could this be the culprit?

Where is this located on the car and is it something I can change out myself or will have to let a mechanic do?

Also, what is the difference in a PCM, an ECM, and an ECU?

I have roughly 90000 miles on the car. So far, my main troubles have been replacing front hub assemblies....
I'm gonna be on a road trip at the end of the month and really need to get this straightened out.... don't want to end up stranded a long way from home. Any advice would be greatly appreciated.
Thanks..

[JTrujillo86]

If it is the PCM, you would need a mechanic to do it. After they are installed they need to be setup by a computer.

PCM = Powertrain Control Module
ECM = Electronic Control Module
ECU = Electronic Control Unit

I believe they are the same thing; people just refer to it differently.

Jeremy

[aleroaddict]

Hey man, I just got a 99' Alero a few days go, a few problems already!! But one of them was the clicking, smiliar to what you described. The guy I bought it from replaced the Intake Gasket seal because it was leaking. Then after I drove it one night, it started clicking when I got home. (by the way, I have the V6 3.4L) The next day, he looked at it. It turned out that one of the push rods was clogged which was preventing oil from circulating throughout the engine. One of the valves or something was clicking. He blew out the push-rod with like an air compressor, and then the oil circulated and it was fine.
Hey, good luck, I hope that I helped!!

[DamienZ28]

I have the same problems randomly dreded lifter tick really annoying I did a motor flush and blew it all out with a compressor and problem solved.