loss of power

[ik2290]

Ok im new to this forumns stuff so bear with me. I've got a 2000 7.3 f250 SD 6 speed 4x4. Last night I was headed home, while on the on-ramp to the highway I razzed on it and nothing happened. the rpm's didnt come up, the speed increased but VERY SLOWLY. Its just sluggish. When I got to a hill I had to downshift and was still losing speed. Turned my chip off (ts 6 position) thinking that might be a problem, didnt do anything. Oil pressure gauge was where it always is, fuel filter was changed about 4k miles ago, has half a tank of fuel in it. When I got home I turned it off, restarted it, and let it idle for 5-10 minutes listening for noise, watching gauges ect. Put it in gear, took off down the road, ran like a champ, no issues. What in the hell is going on? Opinions? Suggestions for things to check? Any advice is greatly appreciated.