2003 Mazda Tribute Idles Rough Won't Accelerate Over 10 Mph

I have a 2003 Mazda Tribute 3.0 liter v6 just replace the the rear piston and the heads put everything back together and drove it around and it worked fine then drove it the next day and it started fine and drove it to a friends house and it sat there for about 2hrs and the started it and it drove fine for about 5 minutes and then even with the gas pedal all the way to the floor it wont go above 10 MPH and then it stall what could be the problem