92 Isuzi Rodeo Trans Problems

Hello All Any Information Would Be Greatly Appreciated . I Purchased A Good Running Rodeo From Ebay. I Found If I Didnt Deactivate The Alarm Before Trying To Start Vehicle A Few Times The Vehicle Wouldn't Move I Would Have To Close All The Doors Reset And Deactivate The Alarm Then It Would Move .sometime I Would Have To Disconnect The Battery In Order For It To Move It Seems To Be Trying To Move In High Gear . I Changed Filters And Fluids To No Avail I Was Told It Could Be The Alarm Or Short. When I Does Work I Can Ride For Days Before The Trans Light Starts Flashing And Having To Disconnect The Battery To Reset Whatever Is Wrong Is This Common With This 4l30 Trans ,also If I Manually Shift It It Ride Ok Just Have No Over Drive Till I Reset It By Diconnecting The Battery Thanks For Any Info On This Problem I Hope I Explained It Clearly