Well welcome to RCT!
I have a pro4 myself and a few others on here do also. Pretty good truck both for the track and bashing.
I really don't have anything mechanical driveline and suspension upgrades to recommend as mine (loaner truck from a buddy of mine) is all mostly stock besides electronics and it's plenty durable. I did break a arm once but I replaced it with another OEM one, driver error on that one, but if I had to upgrade those I'd go with RPM. (If they have parts for the pro4, not sure)
A faster and more durable servo is always one of the go to's. I got a savox in mine but can't remember the model, but it's apart in the black series/lineup of their servos. Quite expensive but really good gear. NitroPro is also up there too.
For racing id upgrade to a higher grade sensored system as the stock reedy electronics are pretty meh. In mine I run a HW 10BL120 G2 SD with a older (discontinued) HW 3656 4000kv sensored power system. It has tons of torque and flies.
HW
Max10 G2 140A/3665 would be a really good combo, for between a track racer and a at home basher. Waterproof and sensored. (Note, these are bigger (longer) motors with a bigger motor shaft so you would need to supply your own 5mm bore pinion, as I believe stock on the reedy 3300 is a smaller 3.17 shaft/bore)
Batteries is always something good, CNHL 6600mah stick packs (2s) are my top pick but there's others that are really good for the price.
Tires, #1 thing, when you start racing competitively at your local track, getting the appropriate tires for that surface will help, alot.
Have fun racing!
Edit: something I would also do is tighten up the servo saver (in the steering rack) so you have more of that direct steering feel, at least that's how I like my cars to drive but everyone is different.
#makeshortcoursetrucksgreatagain
