91 300SE tranny slipping?

[sixto]

I noticed this evening that there was less correlation between engine speed and vehicle speed in 4th and possibly in 3rd. I usually do a shade over 70mph at 3500rpm, but this evening I noticed that I was doing a shade under 70mph at said rpm. Also, there was noticeable lag in giving more throttle and getting more speed. Dropping to third, the revs jumped up, but I didn't get the kick I'm used to.

When I got off the freeway, I didn't notice anything unusual such as slippage, lag or flaring. It drove normally the last few miles home. When I got home, I checked the fluid and it seemed fine (level, color and smell).

I've put 4,000 miles on this car since acquiring it with 129,000 miles. Purchased from an independent who claims to have serviced the car prior to putting it up for sale.

What kind of failures do these symptoms suggest? Does this sound like something an adjustment will fix, or is this the tranny's swan song? C'mon, be blunt. I want to practice my reaction before taking it in to be checked.

Thanks,
Sixto
78 450SEL ... just got a new tranny
91 300SE ... next?