[psych0s1s_r3b0r]

Just purchased a 92 Subaru SVX w/152000 miles a week and a half ago... Already love the car and have read up much on here and elsewhere on the issues it potentially has, but that with such being addressed, the car will very comfortably last a long long time...

So here's what I have going on...

Initially, everything shifts and runs very smoothly (not worried about the engine right now, runs beautifully) - did all the time up until about 5 days ago... It still shifts and goes very smooth initially, for the first 10-15 miles at least - but then one or more of the following start happening...

1st -> 2nd - shifts hard
2nd -> 3rd - slips
3rd -> OD - rear end shudders

(think I mapped that out correctly...)
My best guess right now, being a newbie, and based on what I have read is that given it only does it after getting warmed up and I don't know what kind of fluid or really, just how good what is in there is, it isn't a failing transmission (yet), it is a fluid problem that will shortly lead to a failing transmission - mainly because it shifts perfectly for awhile and then after a while, especially much stop/start accelerating, one or more of the above symptoms kick in.

I purchased a transmission filter and some Mobil 1 Dextron V Synthetic fluid (based on what I read on here, seems this is the next best thing to Amsoil which is what I plan on using next, but don't have the time to wait for it as there is nowhere near me to purchase it) - I plan on changing the fluid later this morning (as it is 3AM here) - doing some other minor tune up/changes at the same time (Oil change -> Mobil1 filter / valvoline maxlife synth oil --- fuel filter --- air filter)

So, with all that said, my questions are as follows...

1> Thoughts on my transmission problems? Am I correct in assuming (or hoping?) that it is just a fluid problem - I'm sure I'll discover later today to some extent, but I still would like to hear from people far far more experienced than me...

2> I've read about adding a transmission oil cooler - recommendations and how to's? What are some good models, where do I order for how much and how do I install?

3> I've also read about a modification / add-on that works with the transmission line pressure - removes a resistor and matches the line pressure with the engine activity to have less slip on harder acceleration, but still allow smooth shifting and gear finding on deceleration... Thoughts / opinions?

4> What else can I do (affordably) for this car to last and endure? I don't have much in the line of cash, and I plan on taking a 4000-5000 mile trip in this car at the end of May... I only have a couple hundred $$$ left to be able to work on it - so I really hope no one comes back with a rebuild is necessary... if it is, then it is and so be it - but I really really hope not... Definitely looking for honest appraisals though... and from what I've read on here, there be some people who know what they are talking about floating around...

Looking for feedback and how-to's... Thanks!