Acceleration

After clearing the P0304 code, went on a 45 minute test drive. The code never turned back on, but I did notice something that was off. When accelerating my tachometer would rise to 3 rpm's but just sit there and the odometer would move the same as if I was just barely on the gas and yet when at a semi constant speed (would drop 10 mph on hills) I was sitting at 2 rpm's instead of the usual 1.5. Is this cause for concern? Plugs, wiring, exhaust, and radiator have all been worked on and I know that it isn't causing this, but the acceleration issue reminds me of when I immediately needed to replace the muffler. Help, please.