89 K1500 Cylinder Compression?

Hey guys, I'm new to the forum and pretty new to auto repairs. I recently began having problems with my truck. The engine would turn over, but then would die. I just had a new fuel pump and filter installed, but the problem hasn't gone away. In order for me to drive it, I have to keep one foot on the gas and one foot on the brake, so when I come to a stop, I have to maintain the gas. The mechanic mentioned that it could be a problem with the #3 cylinder compression. Does this sound right? Also, if I was to get this repaired, does anyone have any idea how much something like this could cost?

Thanks in advance for any help or advice,
Mark

Is Your Truck Tbi? It Could Be The Iac Valve Which Is The Idle Air Control Valve. It Allows Air To Bypass The Throttle Plates When At Idle. It Is Located In The Throttle Body At About The 10:00 Position If Looking At It From The Front Of The Vehicle. I Have More Background With Fomoco Vehicles But Just Bought Myself A 90 1500 For A Project. So I Am Learning As I Go Along. Hope This Helps

Check for vacum leaks around the base of the TBI unit and check to see that fuel is coming out of both injectors of the TBI unit also.

Losing compression in one cylinder of a small block V-8 would only cause a misfire (rough idle) condition. How did your mechanic determine that there was a problem with #3 cylinder?