I can't help specifically on your year, but I recently had an experience on my 2003.
I bought it used so I don't when the last service had been done and I had foolishly went way past the recommended interval, assuming it had already been changed once at 60k.
It had started to slip just a little in first but not every time, just occasionally.
Doing some searching, I came across a product called Auto-RX. After reading all the positive reviews at other automobile related websites, I decided to try it.
Well, all I can say now is I will use this stuff on every car I ever have from now on, whether I buy it new and use it exactly on it's first recommended fluid change or on future used cars.
Some people may call it snake oil but I don't care what any one else says, the stuff is amazing. It's not an additive, it's a cleaner and it doesn't change the viscosity of the fluid and it's very gentle. The transmission hasn't slipped a single time since I used it plus it shifts much more smoother it's like a different van.
It doesn't fix something that's broke, I realize that. And it doesn't 'patch' anything that's loose, cracked, etc. It's a cleaner.
I used it in the engine too on my T&C and my 93 S10 Blazer S10 and gained a couple of MPG's and on my 93 Blazer, it gained some HP too. I noticed the oil filter on my T&C was about 3 times heavier than usual from the sludge it cleaned out.
I don't work for them or have any interest in promoting them. The stuff is just good and I am excited about it. Google it for the website as I don't know if I can post that.
There will be some who will respond to this post saying as long as you do factory maintenance that's all you need and I'm not going to argue that. But for the low cost and proven results through testimonials it definitely is something to look into.
Oh, Google 'BMW 60k oil change' and you'll find a forum post about someone who bought a brand new BMW and didn't do an oil change until 60 thousand miles (said no one told him he was supposed to have the oil changed LOL). They took the valve covers off and it looked liked thick mud. They scraped out as much as they could and ran two treatments of Auto-RX through it. The engine was saved, it had no issues and the engine looked like it was new afterward.
Sorry for the long post, it's late and I can't sleep LOL
