Blazer with transmission issues?

My blazer has about 133k miles on it. Just got an oil change and replaced the serpentine belt earlier this week. The "Check Engine" light comes on ever now and then and when it does, here is the issue:
The truck doesnt want to accelerate (from a stop) it seems to start in something other than first gear. No smoke, strange noises, or leaks. This lasts a day or two and then the truck is fine for a few days, then the cycle repeats. Do not know if there's a connection, but sometimes when I turn the truck off the ignition wont go to the OFF position.

I'm not sure you're having a transmission problem. This is a tough one without more information or driving the car. I'm wondering if you're having a problem similar to the thread on acceleration problems not transmission. Check out the link below.
I just replaced my tranny at 158,000 on my 99 4x4 Blazer. They do go out, but my simply went. No first gear, no reverse...probably a broken sunshell gear (clam)..whatever you call it. I would read the attached thread and look at the O2 sensors, MAF sensor, or fuel pump for loss of acceleration problems.

http://www.automotiveforums.com/vbulletin/showthread.php?t=1012635

Hope this helps.......

Take your car into the parts store and have them read what codes are stored....then post them here. That would definitely help solve the problem.