having some tranny problems!!!!

My wonderful 1992 XLT king cab 4x4 ranger with a 4.0 is starting to worry me. It has 173,00 miles on her' and she has all of a sudden decided that she wants to be shifted into over drive by hand???!!!!! (here's the routine)...I have to get up to speed and let off the gas, shift into neutral, let the RPMs fall to about 12-1500 ,bump it back into over drive......and go slowly back into the gas! the RPMs will rise to about 22-2500 because it is now in drive but it will complete the shift ...slick and solid into overdrive.....I am confused about this and today I realized that the tranny will not shift out of 2nd gear unless it is put into the overdrive position(if put into drive , it will stay in 2nd gear)??!!!:rolleyes I need help fellas (I talked to a fella I know from the ford dealership and he said just put a new tranny in it:rollin . I just love talking to some of those folks (instant cure...replace with high dollar part) ! If anyone has an idea , I'm all ears!!!! ps. I baby this truck because I bought her' new and I just cant see putting 20 grand into another truck that will get the same mileage, and drive the same 18 mile round trip 5 days a week, and play the same radio station! I hesitate to put an additive in the tranny because I know nothing about these "snake oils". I have changed my tranny fluid every 50,000 miles. help me keep the ole' girl running,....:hat

it sounds like the tranny is slipping. honestly for as many miles as it has on it and if it's the original tranny it's done you good. when it starts to slip all you really can do is replace it. other gears will slowly go out. I've been there too, have a broncoII with 140,000 and had it replaced once, 2500.00 but it's cheaper than buying a new car!