2002 Chevy Suburban SLIPPING

I HAVE A PROBLEM I CANT FIGURE OUT , WHEN I DRIVE ON THE FREEWAY FOR MORE THAN 20 TO 30 MINUTES , WHEN I EXIT MY TRUCK JERKS ON THE SHIFT , USUALLY PRETTY STRONG ON 1ST AND 2ND GEAR , IT DOESNT HAPPEN WHILE IM ON THE STREET , AND I HAVE DRIVEN FOR MANY HOURS ON THE STREET . I HAD MY TRANS FLUID CHANGED AND IT DIDNT DO IT FOR A FEW WEEKS THEN MY SERVICE ENGINE LIGHT CAME ON AGAIN AND IT STARTED TO JERK AGAIN . WHAT DO YOU THINK THE PROBLEM IS ? THANKS

SHAWN