Someone please help, having probs with 03 Silverado

Someone out there, please help me and tell me if you are experiencing these problems with an 03 or similar year model of Silverado V6. I bought the truck brand new and had no problems with it until recently. The motor will surge when letting off the gas and reapplying the gas slightly. The Tach will fluctuate rapidly up and down (with the accelerator remaining constant pressure. No acceleration is happening yet the tach is fluctuating) between RPMS up and down and you can feel the truck surging as if trying to catch the gear or something. I thought it may be the tranny. Took it into the shop and they flushed it all out (26k miles on it right now). They also hooked it up to a computer and said GM had issued a problem with shuddering and said they "fixed" it. Big surprise, it's still doing the same thing.
I have had this truck in the shop 4 times. I am going in for a 5th, but this is it. If no fix happens, I am giving up. I have read other similar problems on this message board. I am glad to know that I am not alone in this. It is beyond frustrating to pay for a brand new vehicle and have it perform like this. I am deeply disappointed. I have always been a loyal Chevy driver, but this is making me skeptical at best. If anyone has any info for me, please let me know. I think its either the transmission or something with the fuel or motor system. Possibly a computer chip. Like I said, dealer always says it's "fine."

My girlfriends V6 was kind of doing the same thing except it was when she pressed the brakes in. after 2 weeks in the shop we found the problem the ignition wire broke inside of the insulation. So when the brakes were appled the movement would cut the power to the distributer.

I had a truck that had somwthing of the same problem. I had to convince the dealer to let me drive something else while they drove my truck until it acted up for them. Their computer said it was fine the whole time, but after a day or two, it started idling erratically for them. It turned out to be a throttle position sensor. Maybe they can do something like that for you.....