I have had my car for about 8 months, beforehand it was my uncles who is a car mechanic. The car has about 280,000 miles on it; however, the engine was replaced at approx. 200,000 miles (my uncle rebuilt one to give it more ''power''). Anyway, last fall I noticed the acceleration on my car started getting sluggish. Right away I thought about my transmission and since then have avoided driving it for more than 10-15 miles at a time and rarely over speeds of 30 mph in order to conserve, if thats the problem, the transmission since I'm a full time student and can't afford to pay for a new one. However lately I've been questioning the problem. The car seems more sluggish when in D3 instead of D4 and I was told it usually is the other way around. Also, when driving the car running errands, the car will " warm up" and the issue is not as apparent. I can drive up to speeds of 60+ as long as I ease into it -- " warm up" here, too. It just does not like to speed up right away. There is usually some knocking and occasionally a grind noise when I accelerate too fast but its not constant. Do you think its the transmission? Or could it be something else?