I have a 2000 Blazer its a 6cyl, 4.3 vortec, with a 700r4 tranny.Not throwing any codes. The problem gets worse when the truck gets warm. At idle there is a rattle from under the truck like somethings loose and it acts like its dying the miss is so bad. But if i hold the break and give a little gas rattle goes away. But when i accelerate it has no power. Took it on the highway and never got it over 50mph and it acted like it wasn't shifting. And at the point its suppose to shift, it felt like i was peddling the gas ( u know pushing the gas and letting up over and over so that the car lunges forward). So I unplugged the MAF sensor and the speed improved. I actually got up to 65mph. It shifted hard from 1st to 2nd. The miss was still there and it stilled lunged at times. I have replaced the EGR, coil and throttle body there was no change. Also ran compression and its all good. Please any advice is appreciated. Now I was wondering if the converter could be stopped up causing this problem its just a thought. My boyfriend keeps telling me its in the tranny but I'm hoping that I'm right for the sake of the cost

 

You're probably right on the catalytic converter restricting the exhaust flow, especially if it's the source of the rattle.