Mitsubishi Repair: 1997 Diamante Auto Trans Problem, shift linkage, necessary pressure

Question
I have a 1997 mitsu diamante (my wife's car) and she went to go to work and put it in reverse and went nowhere.  when I was able to look at it I noticed the trans fluid was low and leaking a little bit. when I tried to put in gear and pressed on the gas it jumped a little bit! I proceeded to get trans fluid and put a quart in, to my dismay it made no difference.  I realized after playing with the shifter that I could get it to go in reverse if you have the shifter between park and reverse?  I read the owners manuel and tried to check the fluid level but the car is parked on a slight incline and I never got an exact reading?  one time low next time full?
I was told to keep shifting through the gears to make the fluid go through everything and build up the necessary pressure but still nothing?  I am at a loss?  about a month ago the car would skip and sputter so I took it to the local mechanic and he said it just needed a tune up but since the location of the spark plugs (below the manifold) it cost us $500.00 for the materials and labor and I would hate to drop a lot of cash for A) to tow the car and B) to have the mechanic look at and tell my transmission is shot! Another question is it gave no indication that the transmission was bad at all, it just happened? plus if some thing was amiss then I would think that the mechanic who gave the tune up and the test drive after the tune up would tell us that the there was something wrong with transmission? but my wife said the car was driving fine up until that morning?  I would think that if the transmission was going bad that it would give us some indication like slipping or haveing a hard time going into gear.  Sorry for the long message and hopefully you have enough information to make a decent suggestion!

Thanks for the time with this

Steve

Answer
Steve,
Because of the sudden problem your wife had with the tranny, I would guess it may be something like the shift linkage may have slipped or broke.  It may just need an adjustment.  It's also possible there is an eletrical problem.  Your transmission's computer may be malfunctioning for some reason.

But to really know for sure, you need to have a mechanic inspect it.  Don't have just any mechanic inspect this.  I would suggest either taking the car to the dealership, or to a transmission shop.  Your yellow pages may list several transmission shops.  These shops are more equipped and qualified to work on a transmission than the average mechanic garage.  Call around to various shops and get quotes.  You can save money if you shop around; and some give free estimates.
Good luck!