I have a 1998 Blazer. Last week our mechanic had to replace the ignition.
I live west of Milwaukee and on Friday was heading to Green Bay. About an hour and a half into our trip the speedometer needle started bouncing around. When we got off the highway, the transmission would not shift. We got gas, checked the transmission fluid ( which was empty) filled up the transmission fluid and it was find, shifting normally. About 20 min up the road the same thing happened. We put more transmission fluid in and took the back roads to our destination. Yesterday we put Lucas transmission sealant in thinking that was the issue. Got on the road today and made it about an hour out when the same thing happened. We proceeded to drive the rest of the way home in 1st going about 20 miles an hour ( yes our 2 1/2 hour drive turned into a 6 hour drive). We kept checking the transmission fluid level and it was fine. About 20 min from home we pulled in for gas and all of sudden it started shifting normally again.
Any thoughts?

 

every time you had problems,was the speedo going nuts? your trans bases the shift points off of the speedo. Replace the sensor,which is on the driver side tail of the trans,or on the transfercase if you have 4wd.