Help! 2000 4WD 4cyl 2.7L Auto Trans Diagnostics

Hey Everyone,

I'm new here and cutting my teeth with wrenching on cars.

Just bought a 2000 4WD 4cyl 2.7L auto trans with 223,000 miles on it.

So far my friend and I have replaced the belts, a fresh oil change, a new air filter and replaced some bulbs and fuses that needed attention.

I've read on here that changing the ball joints is a good idea, and I want to do that next.

I'm looking for recommendations on where to buy them? I want to stick to OEM parts that will last.

I'm also looking for advice with identifying a shutter in the gas pedal that happens when starting and stopping in traffic. nothing loud, just feels like a shake in the pedal. shifts beautifully otherwise.

My friend and I think it's either the drive shaft center support bearing or potentially needs new transmission mounts.

Any advice with diagnosing the problem and where to buy parts would be extremely appreciated.

Thanks for Reading