I'm 2nd owner & auto transmission went out at 92k miles. Local shop replaced w/rebuilt, but transmission would jerk violently around 40 mph. Immediately took back to mechanic & he said it was "low on transmission fluid" & added. Drove 5 miles, still jerking. Picked up mechanic and took for drive so he could feel the violent jerking. He then said it just needed to be driven and would "smooth out" after 1k miles. Truck was idling during discussion with mechanic and I heard what I thought was a manifold leak; mechanic said I was hearing my A/C going out, but then walked to R back side of truck and gave my tailpipe a hardy kick, which did eliminate that particular noise for about a minute (he had not reinstalled the tailpipe correctly after replacing the transmission). Drove about 10 miles and transmission jerked the truck so hard that it felt like someone had rear-ended me. Took the truck to a local Ford dealership & they confirmed there was a problem w/the transmission & they reported I now have a bad manifold gasket on R side. Took back to mechanic and demanded he install a different transmission and fix manifold gasket since Ford suggested all the transmission jerking likely damaged the manifold gasket. Turns out the 1st rebuilt transmission had a "shift kit," which the mechanic said meant it was for a standard - but claims he had no way of knowing prior to installation. Now have 2nd transmission installed, but heard definite rattle under R floorboard area and mechanic said my R catalytic converter is going out, but to go ahead and drive 1k miles so he can change transmission fluid. I'm leaving Thur am for a medical appt in Dallas and will travel about 900 mi round-trip. Based upon what I've read on this forum, I fear driving with a bad CAT could cause damage to my engine... Three questions:
1. Could the violent jerking of the truck when the 1st rebuilt transmission was installed have caused damage to the catalytic converter?

2. Could the mechanic have caused damage to the catalytic converter when he replaced the manifold gasket?

3. Is it safe to drive 1000 miles with a rattling catalytic converter?

I LOVE my truck and there was NOTHING wrong with it until the transmission went out - and now it feels like the problem(s) have snowballed! I know very little about mechanics, but I don't have a good feeling about my mechanic, even though he retired from Ford and claims to have been a mechanic for about 20 years and a parts manager the remaining time. Please help and thanks in advance!