Whats wrong with my nitro rustler 2.5?

About a month ago i bought a Nitro Rustler 2.5. The first day i had it it worked excellent. I took my time and broke it in properly as stated in the book and thought all was well. I did everything as needed. I cleaned the air filter ect. Now when i go to use the truck it works great for about 5 minutes then it will bog down and the Idle will get high and low and then eventually die. What could be my problem? The engine still has excellent compression and ive been cleaning it it WD40 as per the instructions in the book.