IMO, these are the necessities to make it last awhile before needing repairs:
"NEED List"
ACNCM Bulkheads
Front $33 Rear $33
RPM arms $40
RCS Skid plates
Front $18 Rear $18
New Era 3-point roll bar $40
These are my suggestions just to improve things for better reliability, improve handling and less maintenence/broken parts:
pro-line steering kit $40
hitec 645MG servo for steering $40
FOC (removes reverse) $10
Center skid, helps eliminate chassis flex and protects trans/brakes $11
Better cooling head if you have the 2.5 and want to keep it $40
Better engine mount $23
Stay away from big blocks. If need be, go with a decent 18 (os cv-r(x) is pretty solid). Also, if it says integy, don't buy it. It may be cheap, but it's also junk.
Unfortunatly, the t-maxx is a truck with a lot of weak spots for a serious basher. It's quick, handles well, but breaks easily. The bulkhead/hingepin design sucks. The skid plates snap upon impact and the bulks shatter upon impact. The shocks and shock towers hold up pretty well though as do the turnbuckles. Although, I broke a lot of the turnbuckle plastic ends, but pro-line used to make a heavy duty end that was much better. I can't find a link for those though.
I had a maxx for a couple years. I had bought all of the above parts and then some. It was a good truck with the "need to have" list with a small block in it. But when I converted to a 21 BB, the driveline went to crap on me and I was constantly rebuilding diffs, cvds, trans, clutch, spurs...
Stick with a small block and a few key upgrades and you'll have fun. If you bash heavily (lots of jumps and wrecks), get the "need" list and you'll be a lot less frustrated down the line.
If in the end you want more power and a lot of it, do not be tempted to throw a bunch of money at the maxx to get a 21 into it. Save up and buy a truck that starts out of the box with a big block. There are a lot of them around now and it's a much cheaper and better way to go.
HPI Savage
Associated MGT
Losi LST
HB Lightning Stadium
XTM Mammoth
XTM Mammoth isn't the best, but they just released a new version that appears to be much better than their first version, so it makes it onto my list of decent trucks to look at.