transmission service question

I recently changed my tranmission oil and filter.  Beforehand the transmission seemed ok but after it seems like the brake is on.  It runs fine but it did drop 2 mpg  18 vs 20.  I am wondering if it is just the new fluid or perhaps there is a leak at the little seal where the tranmisioon filter goes.  I did not replace the seal, just pulled the old filter old and popped a new on in.  Should i go back in a replace it.  Do i reall y have anything to worry about?  Thanks for another view.

I always recommend replacing the seal when the filter is replaced but I doubt that's your fuel milage problem.
If you've dropped 2 mpg perhaps it's due to the weather, it's colder now and the engine will run rich longer til it has time to warm up.

I didn't replace the seal because actually i didn't realize that there was one in there.  The drag effect seems more like the transmission is just tighter feeling, although there was a noise on accetaration that i thought was valve noise that has gone away with the fluid change.  Perhaps the tranmission is sounding like it should be.  I have about 222,000 miles on the truck now while i put on about 110,000 of those my self.   This was the first ti,me it was changed since i got it.