96 4 cyl auto maybe running on 3?

pretty much feels like a sling shot between gears. is over reving and just doesnt' seem to want to shift sometimes. then once it does shift if really moves. i first want to check the plugs and make sure they're all fine. if that fails then maybe approach the injectors? does anyone have any tips or suggestoins on getting at the plugs or suggestions on what this might be?
thanks
c