Tranny not shifting

I just bought my first Jeep and love it! Its an 87 Cherokee Limited with 200k on it but only about 45k on a rebuilt Staight 6.
When I got it, it wouldnt auto shift.I had to manually go into 1-2, than 3 and then drive. After 4 days of driving I backed out and put it in D and away I went. The 4WD is working fine (at least at low speeds in snow on the back 40) but it seems to want to hold 3rd a bit long and seems to grab a bit on the downshifts between 3 and 4. This hasnt been a problem yet but feels like it might cause a bit of traction loss on slippery roads.
Any ideas on what to look for will be greatly appriciated.

Does the TCU (Thansmission computer) have power. It is located under the passanger side dash. It has a fuse. Small 4"x4" box approx. It tells the trans when to shift. It sends power to the two shift switches.

Take a lok at the tps sensor ....make sure its clean....REadjust the throttle kickdown cable and if that doesnt help replace the tps sensor on the engine throttle body its real sensitive.

pete