2000 Transmission issue Service Engine Soon light on

Greetings,

Please pardon my brevity and my lack of thorough search. I have a difficult circumstance. I am 500 miles away from my 2000 Venture that is experiencing problems. My son has it on the road up in Bar Harbor Maine on a camping trip,.I am away on a trip in the other direction.

It has 130 k miles on it, has been very well maintained and has developed transmission issues.

Here is the sequence of events that has taken place so far.

The SES light came on last night and there was no apparent affect on the driveability of the car. They parked the car for the evening. The next morning they drove one mile to a trail head. On the way, the light went out. Again , no driveability issues. On the way back to the campground my son described the following.

SES light on. When driving at 55-65 mph, and putting the car under a load (ie going up a hill), it won't downshift to a lower gear and as a result lugs the engine and vibrates. If he pulls over and comes to a complete stop, then continues, the car shifts normally up through all the gears. If it is under a load, while accelerating, he thinks it is shifting harder than it normally does but he is not sure. He is not the usual driver of the car.

If he slows down to about 20 mph but DOES NOT come to a complete stop, and then accelerates, there appears to be no downshifting as he slows and when he accelerates, it appears as though the engine is lugging/laboring. He has to come to a complete stop to get it to downshift to 1st and then go up through the gears.

These symptoms were relayed to me over email so they may not be the clearest. We are both in remote areas and have sketch internet and cell phone connections.

I just recently (30 days ago) repaired both transmission cooler lines that go to the radiator because one had a pinhole leak. I topped up the transmission with 2 qts of synthetic Dexron VI (This is what was put in it when I had the trans fluid flushed and changed at 75 k imiles 5 years ago.).

I am going to have him stop by an auto parts store to have the codes read and see if that gives us more to go on. But for now he is 300 miles from home with a somewhat crippled vehicle.

Are there any other tests, symptoms to look for etc that I can relay to him to try?

Any thoughts, suggestions or comments are welcomed.

Thanks.

Paul.../NH

When is the last time the plugs and fuel filter were changed out?

At 75k Miles.

I really think this is transmission related based on the shift points and the way it is behaving.

I think first thing I would do is stop by a parts store and have them pull that code....

Maybe its the transmission, maybe not, other parts will interact and cause symptoms as well, maybe the cat is plugged? I dunno, what does the code read, from there maybe we can tell a little better where to dig in.