Torque converter size

You definitely at least want to do a flush, but better yet an inspection.

I've run a 3500 convertor in my car and a 4000 convertor in my last car for 20 years without issue with a ton of street and even daily driving miles. IF you have a quality convertor it's not an issue.

More on a quality converter... you are better off with a smaller tighter convertor than a looser larger one. I.e. a 10" that stalls at 3000 vs. a 10.5 or 11 that stalls at the same is desirable. really you shouldn't even have to choose. Call and give them your specs and usage and they should set you up with what you need. Dynamic once gave me a choice on a a 9.5" or 10" that stalled the same. THe smaller one cost a little more but had some added features.