I had a similar problem with a 98 mirage DE. I sprayed the linkage around my throttle cable. Another possibility Clean your throttle body, mine was really sluggish until I cleaned all of the carbon out of the throttle body.
lifters
light refracting
Taking your foot off the accelerator.
its probably the spark plugs, they need to be changed i have an 03 diamante and the same thing was happening to me. I had the spark plugs changes and the problem was solved.
It may me that your brake is on.
Tranny problem.
If its manual that would be the cltuch slipping.
The accelerator pedal. Also known as a gas pedal.
Poor driver judgement and excessive use of the accelerator pedal.
Your transmission does not know how far you have the accelerator pressed. Some cars have a cable that runs between the throttle and transmission to 'tell' the transmission how far you have the gas pedal pressed. Some cars use electronic sensors to 'tell' the transmission how far you have the pedal pushed. It sounds like your transmission 'thinks' your gas pedal is not pressed at all. This will cause the shift points to occur exactly as you describe them. Look for an unhooked cable between the transmission and throttle.
The large amount of energy imparted upon it in a particle accelerator.
hb