98 Mountaineer Transmission?? Need Help/Advice PLEASE!!

Ok, so i will attempt to explain this. I was driving home from out of town and i would ease off the accelerator and the truck would slam down into gear almost as if downshiften even tho it wasn't supposed to.. it did this several times so i put it into cruise controll and it was fine. I get it home and me and my friend take a look at it and notice the trans fluid was a bit low so i put in some TransX and Some fluid started it up and went to drive it to see if it would do it again and it wouldn't go into gear.. Mind you I drove it all the way home (about 30 min) It had no problem upshifting before this. Also there was a LOUD whining noise coming from under the truck and a little rattle (rattle could of been a heat shield). I let it sit for about 2 days.. got in it and tried to get it to drive and the truck drove fine without a single problem would shift up and down with no jerk or anything. About 4 hours later I took him for a ride just to see and it continued to run fine untill i drove it for about 10 min the problems all came back wouldn't shift or anything so i pulled over and it was just reving up and wouldn't go into gear. I shut it off and started it again and it went into gear and I got it home but couldn't pull into the driveway because it went out again... shut it off and started it back up, it went into gear and drove into the Driveway. Now this is all baffleing to me and I have no idea what is going on. I am going to check the transmission screen tomorrow and replace it. I dont have alot of money but i am willing to save to put a used transmission in it but i dont want to spend the 400 dollars on a trans if its not going to fix it. If anyone could help me out with this it would be HUGELY appricated. Thanks for your time.

Welcome to the forum!

Which engine/transmission combination do you have? Is your Mountaineer 2WD, 4WD, or AWD?

I've experienced a friend with a 4.0L, 5 speed auto and 4WD that made an odd rattle as well as a sporatic loud clunk that was a bad transfer case. His never failed to "go in to gear" or shift though.

-Rod

Ok, so i will attempt to explain this. I was driving home from out of town and i would ease off the accelerator and the truck would slam down into gear almost as if downshiften even tho it wasn't supposed to.. it did this several times so i put it into cruise controll and it was fine. I get it home and me and my friend take a look at it and notice the trans fluid was a bit low so i put in some TransX and Some fluid started it up and went to drive it to see if it would do it again and it wouldn't go into gear.. Mind you I drove it all the way home (about 30 min) It had no problem upshifting before this. Also there was a LOUD whining noise coming from under the truck and a little rattle (rattle could of been a heat shield). I let it sit for about 2 days.. got in it and tried to get it to drive and the truck drove fine without a single problem would shift up and down with no jerk or anything. About 4 hours later I took him for a ride just to see and it continued to run fine untill i drove it for about 10 min the problems all came back wouldn't shift or anything so i pulled over and it was just reving up and wouldn't go into gear. I shut it off and started it again and it went into gear and I got it home but couldn't pull into the driveway because it went out again... shut it off and started it back up, it went into gear and drove into the Driveway. Now this is all baffleing to me and I have no idea what is going on. I am going to check the transmission screen tomorrow and replace it. I dont have alot of money but i am willing to save to put a used transmission in it but i dont want to spend the 400 dollars on a trans if its not going to fix it. If anyone could help me out with this it would be HUGELY appricated. Thanks for your time.
Sounds like you are on the right track. I'll bet the filter is picking up the sludge/debris in the bottom of the pan. When the truck sits the suction on the filter stops and the debris will fall back to the bottom of the pan. Hopefully its not too late for a filter change and new fluid.

Sorry for responding so slowly.. One of my friends past away this weekend and i havent gotten to changing the filter yet.. As far as engin i have the 5.0L AWD motor.