I bought another 89 coupe deville 120k a week ago and did a tune up including the transmission filter and when driving it for the second time yesterday and as I was on the highway I got up to 65 and had trouble staying there and then getting back to 65, like the engine may have been running high on rpm. So I got off the highway and a little while later I was doing about 40 and it shifted up/down up/down real quick like it was trying to figure out a gear, and when I got to the light it did it again at 20 mph and then just died and gave me a stop engine oil light and battery charge. I pushed into a gas station and checked the fluid which was all on point. So is this a transmission problem and is it something fixable.
Also I check the fuel center codes and they read strange. one was e52 and one was 344 128