Engine sputters/backfires/no power just after initial start
 

I have a 2000 Blazer. It has about 180000 miles and runs fairly well. It does not seem to have much power and when I initially start the engine it will idle fine but when I begin to pull of it sputters and backfires. Once started it will not do this again until I have to crank it again. This occurs when the engine is either hot or cold. It also seems to lack power. There are no codes. I just ran a can of sea foam through it with no results. Where should I look.

I would look at cat. converter