clogged inlet side of pumps would cause cavitation and lose of power to the drives, not lose of engine rpm. I can't see having a problem on both drives at once. I have seen a similar issue with a drive motor that was binding when it got hot. But not both sides at once, unless both wheel motors are going back at one. little chance. I would be checking to make sure you are not loosing spark or otherwise dropping a cylinder on the engine causing loose of power.