2001 Chevy Suburban loss of power

I had the same problem but I have it fixed now. I found that the car would not accelerate to more than 35 mph, took it to the dealership and they could not fix it, after two days with them I had it towed to another mechanic friend and he told me that the problem was not with the throttle control but with the catalytic converter. Replaced the catalytic converter and the problem went away. And the power has been back. The mechanic also told me that I need to get a tune-up on the engine and flush the gas system to prevent the new catalytic converter from clogging. Did all he suggested and after 2000 miles not only is the power still there but I'm getting around 19 - 20 mpg on the highway, the vehicle runs like new again. Hope this helps you as it did me.