At about 40,45,50,55(sometimes 60) mph the car lugges forward like it is shifting. I noticed that it is getting worse and it all started about the same time my tach needle started bouncing a little. Please help. could it be a gear in the tranny? Rearend (I do spin'em hard every once in a while)? Computer? I'm totally lost and broke. Please reply as soon as you can. thanks

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late model 91 rs
fully loaded t-tops
red leather
paint- gm red and yellow blend (light red)
custom pink rims
305 tbi k&n,computer chip
MTX sub and amp (very loud)
vic_v8@yahoo.com