What exactly are the symptoms that you are experiencing which leads you to believe that one truck is geared differently than the other?
Lack of torque?
One is louder than the other?
What engine are you running in each truck and how many miles on each engine?
Going to 3.55 gears will reduce your RPM at highway speeds, but like many modifications, there is no such thing as free lunch.
You lose considerable torque in all gears, especially in low gear.
This will be very noticeable with a well-worn engine, or one out of tune, or carburetor is out of adjustment.
