what could be the problem pag may ugong yung car pagdating ng 60kph? kanina ko lang kasi napansin while going for a long drive. basta pagdating nya ng 60kph ay may kakaibang ugong kang madidinig. you can feel it kahit sa accelerator pedal. para bang tunog pag nag-engine brake pero consistent. pag below 60kph ay nawawala naman yung ugong. although smoooth naman yung andar ng engine at wala naman vibration sa body. naitakbo ko siya kanina for 200kms. at 1st, kala ko yung gulong but pinakinggan ko mabuti at hindi naman yun..
sorry but ang alam ko lang kasi ay mag-drive at no knowledge ako pagdating sa troubleshooting. so please, i need your advice...

it's a '01 Revo 2.0L Gas A/T
mileage - 64,000 + (last PMS was at 50k)
tires- bridgestone (about 6 months old)

could it be the tranny???