[AirSpeed]

I installed a GM crate 350/290 hp engine in my truck about a month and a half ago and have had nothing but problems, starting with receiving an engine with broken valve stems. They sent me a new one but o was without my truck for nearly a month and it's cost me an extra thousand bucks so far. The engine has zero power even after a new carb, distributor, plugs, wires, ignition, everything is new but the engine is gutless and gets almost 4 mpg, closer to 3 most the time. It runs incredibly smooth and sounds great but it's a dog! I've taken it to three shops and no one can figure it out, the last guy, who still has it has been working on it three days straight with no luck. He just installed the exact same engine with the same components I have in a truck identical to mine and that truck is strong as hell. The carb and dist are the ones Summit recommends. The only thing we can figure is there's something wrong in the engine itself, even checked the timing gears.
I got to reading the warrantee and it says it has to be installed by a licenced shop in order to be covered by the warrantee, is this something Gm and summit are going to stick by? Or is there a possibility they will do something? I didn't want to bring up the warrantee to them until I was a little more educated on the warrantee.
Thanks for any suggestions!