1993 4WD 2 Door Sport Blazer -- Did dealership rip me off? Any recourse thru dealership?

I recently traded in my 1993 4WD 2-door Sport Blazer, 136K miles, very good condition w/exception of small rear fender dent which only slightly impacted dropping rear door. Was fully loaded -roof rack, AC, running boards, tow package, inside very clean & no damage, tinted windows, power door, power windows, power mirrors,ABS,alloy wheels, radio w/cassette, rear wiper, etc. etc.  Check engine light had been coming on (on and off) for about 4 mos; never investigated the reason for that, though. Also radio and clock digital came on but didn't work (it was always "1:00" and "98.5 FM"! Traded it in at dealership and only got $2500 + tax (about $2700). Manager at dealership snapped it up immediately after I traded it in.  I was looking at Kelly BB and now see everyone sells these trucks for about $6K.  I feel cheated, although I guess I could have walked away.  Can't stop kicking myself over this!  Could I have gotten much more for a trade-in at dealership, or was I ripped off, and is there anything I can do to recoup loss (thru dealership, etc)?