99 Blazer Hesitation

I have a 99 4x4 4-door. This only happens for about 10-20 seconds after I start the truck if I do not let it warm up. I try to put on the gas and there hesitation. No power. Due to the fact that it is only for the first 20 seconds I am thinking it might be some sensor that is taking a little while to get warmed up? Has anyone else encountered this? Any ideas what it could be?

What engine and mileage?
What is the tune up history?
Fuel filter and fuel pressure OK?
What kind of air filter and plugs?
Any codes or check engine lights?
MT

It is the 4.3 V6, 88,000 miles
It has had a normal tune up history.
Fuel Filter replaced about 20,000 ago
Fram air filter replaced 10,000 ago, Bosch Platinum plugs and wires replaced 15,000 ago.
No codes or check engine light.
Replaced catalytic converter and O2 sensors about 5,000 ago, could this have something to do with it, but problem was occuring before this.

Thanks for the help!

It might just be the plugs. Our trucks have a tendency to be a little picky when it comes to plugs, it is best to use genuine AC Delco Plats. Make sure that they are properly gapped.
Additionally, you may want to clean your MAF - just search the forum on "clean" + "MAF", and you will find easy to follow detailed instructions. Very easy.