seanoc

I have an unusual problem. On first start up from cold (So Cal cold) intermittently, there is a thump in the exhaust somewhere near the drivers side. It does not sound mechanical, more like fuel in the exhaust popping off and the car lurches slightly. If I start it the normal way it often gives the thump then runs roughly for a few seconds then clears itself to a fast idle and all is well. I discovered another way to start it that seems to by pass this problem most of the time. I bump the starter briefly, turn off. Then start normally, it fires right up as if it were brand new to a fast idle. It started doing this right after a transmission overhaul about 4 years ago. The transmission works perfectly. The transmission shop sees no relationship to the trans overhaul, I can't logically see it either although he did suggest an injector leaking down overnight very slowly. Can this happen? I do check for fuel pump buzzing when I turn on the key. It stops in about 2 to 3 seconds. I have lived with this issue for 4 years because it is expensive to take it in and say fix it. I know they will do a full tune up and replace parts, diagnostics etc and hand me a bill for $4000.00. The car is in very good shape and the problem doesn't effect drive ability at all so I have lived with it. And of course a 2002 Tahoe is only worth about 3 grand or so.OH yes I did tell the tranny people about it right after I got it back but they wouldn't take responsibility for it. I just discovered this forum and thought somewhere in this great database of experience there must be someone that has seen a similar problem. I'm thinking injectors but not sure. Any help or suggestions will be greatly appreciated. I can do the work myself as long as I don't need to get underneath.
Thanks in advance,
Sean