In the time I have owned a Redcat Racing Ground Pounder I've broke a few things my list and my step fathers can be found here . Link
The first thing you should look in to upgrading on the Ground Pounder is the motor :
Really I find the top speed pretty good but I feel the truck needs more torque for driving in grass and driving off road .
My recommendation is a 550 motor with 19-22 turns here are a few examples :
Redcat Racing Part # 28446 sells for about $16.99
Traxxas Titan (21T) Part # 3975 sells for about $21.49
Thunder Tiger part # PD9221 sells for about $27.99
My second upgrade I recommend is to upgrade pinion and spur gear .
Part # bs801-014 is a 43 tooth mod 1 spur gear made from a composite plastic that can replace the stock spur .
About $10.00
Part # MPO-017 is a steel version of the BS801-014
About $14.00
Now you will need at least 1 pinion that has a Module 1 tooth profile . If you are using a motor with a 1/8th inch shaft " like the ones listed above " here are a few options.
Pinion Gear, 9T/12T x 3mm, Mod 1 part # ECX232028
about $13.00 for a pair
OFNA 3mm Bore Mod 1 Pinion Gear about $12.00 each
11 tooth = Part # 21316
12 tooth = Part # 21314
13 tooth = Part # 21315
14 tooth = Part # 21306
15 tooth = Part # 21311
16 tooth = Part # 21312