trans or computer

My trans sometimes jerks when accelerating. Some days are fine, others are not. Also, it will slow down the car when coasting to lower speeds when its downshifting. I changed the filter, didnt help much. Then I changed the trans, and it was good for about two weeks, then started doing it again. Could it be the computer ? I mean my intrument display is doing strange things, mpg sometimes says 99mpg ( I wish ) , steering (http://rover.ebay.com/rover/13/0/19/DealFrame/DealFrame.cmp?bm=882&BEFID=422&acode=848&code=848&aon=&crawler_id=460869&dealId=X0u4JYHHnCOKq6Jklufbww%3D%3D&searchID=&url=http%3A%2F%2FWWW.XTREMEDIESEL.COM%2Fpsc-sg753r-ported-steering-box.aspx%3F&DealName=PSC%20SG753R%20Ported%20Steering%20Box&MerchantID=460869&HasLink=yes&category=0&AR=-1&NG=1&GR=1&ND=1&PN=1&RR=-1&ST=&MN=msnFeed&FPT=SDCF&NDS=1&NMS=1&NDP=1&MRS=&PD=0&brnId=2455&lnkId=8070676&Issdt=161008051705&IsFtr=0&IsSmart=0&dlprc=926.25&SKU=29024) sensitivity doesn't work, and the "trunk ajar (http://www.amazon.com/dp/B000E72N72)" warning beep is driving me crazy. I heard the computer controls motor, trans, and dash info, so is it possible that it could be my whole cause of everything ? If its not the problem with the trunk warning beep, how can I bypass it ?