'88 Camry transmission trouble

Hey, i've been having some problems with my automatic transmission on my 1988 Camry LE. I tried the search feature, but didn't come up with anything that sounded exactly like the problem i'm having, so here goes... 
 
The car starts out in first, but will jump to 3rd instead of going thru second gear. It also does not shift into OD. The odd part of all this, is sometimes it will shift as is nothing is wrong at all, first, second, third, and finally..OD. The OD button works on the shifter, it will down shift when you accelerate, but then after about 5 mins of driving, it will shift back down into third, and stay there until the vehicle is pretty much at a complete stop. It will not downshift otherwise.
 
Oil is a bit dark, but not burnt. Car has about 280K on it, and i'm assuming the oil has not been changed for a while now.  I bought the car at 260K, and all the shops i've gone to said not to change, as it might do more harm than good.
 
Could this problem be caused by a Solenoid? I find it very strange that once in a blue moon it will work properly. Just enough to annoy me.... it actually works, but just doesn't feel like it!    
 
Any help on this would help alot. Thanks.

I have 91 Camry and have the exactly same problem.
I changed the transmission oil with a filter but it did not solve the problem, so don't try oil.
I asked several auto shops and most of them told me to donate the car and buy a new one.
I was thinking swapping the whole transmission because buying one from ebay costs $400~$500 and the labor to swap it costs around $500.
Spending around sub $1,000, I can get an almost-brand-new tranny.
However, I wonder if swapping the tranny will solve the problem.
Please post any news if you hear more.

Good news, car is shifting fine, and the bill was under 200!
 
Turns out, the previous owner had bent the transmission pan, denting the filter, and a valve body pipe. So after a new filter, valve body pipe, and a shift solenoid, the car is running fine!
 
So unless you've been off-roading in your Camry, or have jacked it up using the transmission pan , i'm sure your fine and it's just the shift solenoid that you need to replace. I'm assuming your pan will have to be removed to get at the solenoid though, so you would need new oil and a gasket, and the labour to install it. Still, it won't be anywhere close to what you where thinking with that new tranny!
 
AT fluid - 26.95
Pan gskt - 8.95
Filter - 12.80
Valve body pipe - 5.00
Shift solenoid - 42.80
Labor - 70.00
 
Then of course all the taxes, and remember this is all Canadian dollars.
 
Hope this helps.

It may sound odd but the problem was solved with another oil change.
I went to another place to change the transmission oil.
This time, they flushed the whole thing before putting new oil.
(Last time, I guess they just drained oil and refilled without flushing.)
The problem solved.

lol i just love it when people solve their own problems!