1999 Mtneer 4.0 SOHC 4x4. 158000 miles. A few weeks ago, it started doing a thing where it would occasionally free rev in drive unless you put it in 2nd or neutral and back in drive. At that point, I checked the transmission fluid, and it was about a quart low. I topped it off and forgot about it. This past week it started doing that again, so I checked the transmission fluid level again, and it was fine. I dumped in a can of Transx, and figured it might just be the cable out of adjustment since bumping it into neutral and firmly back in drive solved it for that trip. I also tested engine braking, and it does not have engine braking in 1st, but does at speed if you turn off O/D. Reverse works fine. Now it's taking a long time to shift out of first (seems to be at least 3k RPM's at the minimum) and, after a few of those, it takes off in 2nd and the O/D light flashes. I'm sure this means there's a code, but of course my Bluetooth OBD adapter doesn't read those. Based on the symptoms, does this seem like something involving dirty internals/solenoids that could be addressed by using a cleaner in the transmission, or does it sound like something more serious? I can't afford to have the thing rebuilt (or even replaced with a junkyard transmission) right now, so if there's anything I can do to extend it's life at this point, it would be great. Up until tonight, when it started the slow shift out of 1st, it shifted fine, no delays or flares. Thanks for reading.