Greg, I am going to assume you have an auto trans because you are worried about it. The EZ or injectors will probably be OK alone, but both together will shred your transmission. Injectors larger than DD2's or equivalent will also shred your transmission. DD2's are the absolute limit for a stock auto, and some have had slippage with just the EZ or just DD2's. Injectors and boxes make different kinds of power. The injectors make very smooth power across the RPM band, a box adds a lot more lower in the RPM range where the auto is more vulnerable because of lower pressures. Go with either, but not both until you are ready to upgrade the valvebody. If you put on either and feel (or see on the tach) ANY slippage get it addressed immediately. A slipping transmission dies in short order. Hope this helps.