car runs fine from cold start, but after it warms up it starts sputtering and missing- temp gauge on dash is fine- but I think the car is running hot. Upper radiator hose has pressure and is hot after engine has been running for a few minutes, but the lower hose doesn't seem to have anything coming through it (no pressure when squeezed, not hot) B16a sir2 just swapped in 2k miles ago- car has been running great until now- any ideas? I replaced the water pump before putting in the motor- maybe thermostat or clogged radiator?