2001 Pontiac Bonneville • 211,000 miles

2001 Bonneville SE with Series II 3800 engine. Just had the catalytic converter replaced a couple months ago because the old one had blockage. The symptoms seemed to be a bad transmission because it was having difficulty shifting. Turns out that the engine wasn't supplying the transmission with enough power too shift between gears. This is putting it all fairly simply but now the transmission issue might be back. The vehicle drives if you run it around 4-5rpms but it will only go a max of 5 miles an hour in either reverse or drive or any other gear. The transmission fluid looks clean it was flushed 50,000 miles ago. I just want to determine if it is the transmission or if that is a known problem with transmissions.
January 30, 2013.

Have a trans guy scan for codes first. He will give a better opinion

Jan 30, 2013.