02 Silverado 4.3 V6. When I have the A/C on, I can feel when the compressor kicks in, a slight addd pull on the engine. But what about when the A/C isn't on? When approaching a hill, I ease down on the gas, the converter unlocks, the rpms increase as they should. But 2 seconds after the unlock, I can feel a distinct pull on the engine, the rpms slow some, and it stays that way until I'm over the hill. The A/C isn't on, but it feels just like when the compressor kicks in. What could cause this?