Hi everybody, I am looking to buy a 2005 GMC Sierra - 161k miles. I don't know much about diesels, and I found this truck I really like. I test drove it today and everything was great until we got to a red light. When the light turned green and I hit the accelerator to go, the truck barely responded. I tried to get it moving for about 5 seconds before I got much of a response. Then, for the next 40 yards or so the truck would not go over 20mph until it seemed to jump back into gear and start working fine again. If I remember correctly, at one point I had the pedal on the floor when we were going 20 and the speed dropped down to 10 mph, then started to climb back up.

I have a buddy who knows a thing or two about GM and diesels, and says it's a great truck and was there for the test drive. However, some people have told me this could be a simple loose fuel filter, or something as big as a fuel system or master cylinder...so I have no idea what to think. I bought a F450 last year (all cash) for work that seemed to have no issues at all, then the fuel system went out 2 months later so I'd like to avoid another situation like that at all costs.

The car fax are good, 1 owner and no accidents. Does anyone have an idea of what kind of issues I may be looking at here? Should I be worried?