reverse and dash question

yesterday i went out and got a ecm and put my two pullable chips from the old one and "voila" but as the day went on the service light came back on, then i noticed when i put her in reverse (4+3 manual tranny) she doesn't want to hardly go, but all other gears seem to be hitting as expected, any clues as to whats going on, also dash lights and gauge lights seem to go on and off intermittently. this is the first time i've driven her due to buying her from the auction with the ecm issue, "but man what power" she will getaway from you if you're not careful.