so the best mods I've found to date are
upgrade the stock steering servo a
hitec 645mg is the bare minimum stronger is better.
Dual disc brakes
throttle linkage mod with ofna sliders
20 wt oil in the stock plastic shocks
tires the stockers are good for bashing but anything else change em out
tie rods lunsford are the best but gpm works as well
the only aluminum part I would recommend are the F/R gear box's from GPM ( not sure if anyone else makes em) these are not the diffs it's the case that the diffs ride in makes the area very strong and helps keep the ring and pinion from stripping due to flex in the stock plastic.
low center of gravity TVP's really help the handling and help to lessen rollovers
light weight gears and titanium gear shafts.
A good engine and air filter
skid plates and tank guards are optional in my opinion.
17mm or 23mm hex conversion is going to be my next upgrade I'm still running the stock 14mm but I've stripped out my share of wheel hexes.