Have a 2002 Case STX 325. It seems low on power pulling a 30ft airdrill. Seeding peas at 2" deep. The 325 has a hard time doing 3mph and any little hill it seems to not have enough power. Runs at 2000rpm and will pull down to 1400rpm on flat land with the drill going. Even going down the road it has a hard time getting the rpms up and a struggle to get to 16mph with the airdrill and an empty cart behind. Its a 2320 flexicoil cart so not overly big. Have changed all the air and fuel filters. Any suggestions?