Do you track your mileage? If its gotten worse, that could indicate O2 sesnor issues also. The stumble could be, as the truck warms upm and lights off the catalytic conveters, the O2 sensor is supposed to sense that, and the engine computer adjusts fuel delivery and spark timing. If its getting bum readings, those adjustments are done blind, with no feedback.
Really, the time spent at Autozone should be under 10 minutes, if they are not busy. All they do is grab the handheld reader, plug it into the OBD port under the dash, and about 1-2 minutes later, they can tell you waht code you have. Have apiece of paper handy to jot down the codes
O2 sensor, depending on ease of access, is usually about a 5-10 minute job. Theres a special socket for them, if your a good wrench with a feel for things, you can try using some PB Blaster and a normal open end wrench, but if your skills are not up to it, you could strip it. Last ones I did were on the Neon when I upgraded its turbo, at 55K, and they came out easy as pie.
I'll take a look at my 99 Blazer and estimate ease of access sometime today.
