I have no Idea what is wrong with my truck

I'm pretty sure that the spark plugs are as old as the truck. I was gonna change them when I hit 100,000 miles, but if you think that it may be an issue with my trucks problem I guess changing them now wouldn't hurt. I dunno what the codes in the computer are. All I know is that after trying to install the programmer my truck coincidentally stopped idling. I've never had problems with this truck before and there were no warning signs. I have disconnected the battery hoping that this will show me if the problem is my truck or the faulty programmer. So, I guess we'll see. If that doesn't work, then I have an appointment at a GM dealership tomorrow morning to have my sytem re-flashed. I am at a complete loss as far as fixing this problem. Let me know what you think. If what I am thinking could be wrong is right? Thank you!

I was told that if the system was corrupted by the programmer that I should re-flash the sytem to take it all back to stock. Which is fine with me cuz it was stock to begin with. I'm gonna go ahead and buy spark plugs today. Are Denso's a good brand? I've heard a lot of good things and I like what I read. But as far as the idling problem, what more could I do if it turns out not to be a corrupted system or the spark plugs? Thanx

O.K. Thanx for all your help. I will let you know what happens after the reflash tomorrow if it fixes the problem or not. And I'll keep those other spark plugs in mind
Tanya

O.K. So I brought my truck to the dealership today to have my system reflashed and the problem was basically my dirty engine! My throttle-body was really dirty so that when the program was installed I guess there wasn't enough air and it messed up. So when the program was taken back off my truck didn't know how to idle. And I couldn't teach it because of the restriction of air flow to the engine and what not. So they cleaned it, reflashed it, and sent me on my way! Yay! So it's all better and I can still use the power programmer! I'm just gonna go through and clean various parts of the engine first, just to make sure this doesn't happen again! Thank you for all your help and I'm gonna go ahead and start the long process of flushing my engine and switching all the parts that need to be switched and upgrading everything I want to upgrade! Thank you again!
Tanya