TRUCK RIDE AND PERFORMANCE?

JUST BOUGHT A 2004 CHEVY 2500HD SILVERADO EXTENDED CAB, LONG BED, 36,200 MILES, RUNS ON GAS AND NATURAL GAS, I DROVE IT FROM SALT LAKE,UT. TO TULSA, OK. AND ON SOME OF THE ROAD IN CO, I WAS GETTING MOTIONS SICK FROM THE EXPANATION CRACKS ROCKING THIS TRUCK FROM FRONT TO BACK, I THOUGHT IT JUST MIGHT BE THE (HD) TRUCK,SUSPENSION IS  JUST TO HARD, ONE MECHANIC SAID I MIGHT INSTALL AIR-LIFT AIR BAGS AND NOT FILL THEM MUCH AND IT COULD HELP STOP THE ROCKING AND MAKE IT A MORE CUSHION RIDE, I THOUGHT SINCE THE SHOCKS ARE THE SAME THAT CAME WITH IT, AND SINCE I DON'T NEED A 3/4 TON RIDE (I JUST WANTED A TRUCK THAT RUNS ON NATURAL GAS 87 CENTS GAL  IN TULSA)  I THOUGHT I SHOULD REPLACE THE SHOCKS WITH Skyjacker Hydro 7000 Shocks OR Rancho RS9000XL Shocks WITH 9 WAY AJUSTMENT., ANYONE HAVE IDEA ON THIS?
QUESTION 2 . SINCE I DON'T NEED 10,000LBS. OF PULLING I THOUGHT OF CHANGING THE DIFFERENTIAL GEAR FROM 373 TO 343, TO LOWER RPM, HELP GET BETTER GAS MILEAGE AT HIGHER SPEEDS, BUT STILL HAVE THE PULLING POWER OF 1/2 TON TRUCK, AND BUY A SCT CHIP TURNER TO HELP ENGINE PERFORMANCE AND GAS MILEAGE, AND SEE IF I CAN MAKE IT RUN EVEN BETTER ON NATURAL GAS, SOME DOES ANYONE HAVE ANY THOUGHTS ON THSE QUESTION? THANKS FOR ANY HELP!