I have been running a Tamiya Pershing for 4 years here is what I would recommend
1. install a Daryl Turner Gear Box plate (you can get from ETO) makes repairing/replacing a gearbox a 20 min job instead of 5 hours.
2. replace 380 motors with 480 motors (gets speed down while improving manervarblity when down to 1 hit)
3. install rubbersealed bearings in the road wheels
4. cut the speaker box down to make more room for the battery (be sure to seal the box so that the bass sounds is preserved)
5. get the upgraded idlers
6. get a Darl Turner IR LED holder to mount in the mantlet