My 98 Ranger's 4R44E automatic actually first started to go at about 56,000 miles and I rode it out until 87,000 miles when it simply wouldn't go anymore. Ford told me the valve body was slugged up, which I was shocked to learn since I had serviced with Mercon 5 more than most people, and changed the filter at the recommended interval. They rebuilt the valve body and it cost me $958.00. About 60,000 miles later after the technician said you shouldn't have anymore problems with it, it's getting ready to go again. Starting to feel the same shudder shifting into second, just like before, but it doesn't do it all the time right now. This time I dropped the service mileage from 51,000 miles like it said in my Ford Service guide to 36,000 miles. I changed the filter and added Redline D4 Synthetic transmission fluid which was equivalent to Mercon 5 and it made the best difference in shifting precisely, but I guess it can only do so much since the transmission is getting ready to go again. I do not feel like building it again and having it go out in another 60,000 miles. Is there any heavy duty parts available to make this transmission more durable. I've got chip, cold air, exhaust, accel ignition. So it's not fast, but it's got more power than a stock 98 2.5, and I'll bet if the transmission was more stout it would be a lot quicker. The trans never could keep up with the power the engine was outputting. I just want to know what can be done to "beef" it up during a rebuild?

 

TransGo makes a shift kit for the 4R44E/5R55E, I know a few of the guys around here have had it installed and like the way it firms up shifts, etc. You can find it in their Application Guide: http://www.txchange.com/sk.htm

Also, adding an additional tranny cooler might be worth considering.