we have purchased 2 harnesses from PSI and we were happy with both of them, ask as many questions as you can, they will do this too, and you will get a good product from them. Your ls1 should be a great swap, just dont get discouraged when you run into the inevitable fitting issues. As for power, my combo is pretty mild, 6.0 block (lq4) ls3 heads and intake, cam from EPS, 1.75" primary longtube headers, almost 500 hp and 473 lb ft of torque. all parts are stock except the cam, springs, headers, oversized pistons. our 5.3l has an ls6 cam and intake and its almost at 400 hp with headers. you are gonna love the power potential of your ls1.