The problem Im having is that for each gear my transmission wont allow me to accelerate past 10 mph increments. (i.e. 1st-10mph, 2nd-20mph, etc.) If I do try to go faster before changing my car starts shaking. I cannot go any faster than 60mph. Dont really know what the problem is. Friend suggested I change out sparkplugs, does that have anything to do with it? Thanks for any help.