97 Jimmy speed problem???

Today on my way to work my 97 Jimmy was driving slow...it seemed like it had a hard time getting into gear and moving at normal speed. I have no idea what the problem could be, but it almost felt like it was in 4wd low, but I checked everything and that wasn't the problem. (No, my parking break was not on either.) Any help would be much appreciated, thanks!!

Did the Check Engine light come on?
Is it driving ok now?
Have you had any work done on it recently?

Yes the check engine light is on.
I have not had it worked on recently.
The problem is still persisting.

...I was suggested that I probably need my transmission fluid replaced so I'm going to do that and see what happens. Thanks for the response tho.

Have the auto parts store do a free computer scan...most chain type stores do it free.You might shift each gear manually in case there's a shift solenoid malfunction.