A guy i know has an late 80's early 90's chevy fullsize lift truck. He currently has 38" mickey thompson baja claw tires and is running 4.56 gears in the back. He wants to go down to 35" tire, will he need to change his differential gear ratio? He also has detroit lockers and if he needs to change his gears will he be able to put the lockers back in and have them work properly?  

Well with 38's he should be running 5.13's or 5.38 not 4.56. With 35's I would say 4.88  to 5.13. The reason I say this is 4.56 is light but a change to a 4.56 from a 4.88 is not much so if I was going to change I would go with 5.13. On lockers, the ping and pinion change does not effect that but a Detroit or its like is a poor choice for a front axle.  

Snoman is right, I myself am running 5.13 with 38.5 thornbirds for off-road use and 35 BFG for on road. I have great acceleration and throttle response to the wheels.  

now that i have more information...it is a 1998 Chevrolet fullsize halfton truck, its 2 Wheel drive on a fabtech 7" suspension lift with a 3" body lift...so with the 38" tires, going down to the 35" tire, what gears should he be running. He also has no front axle since its only a 2 wheel drive. thanks for your input so far its been helpful...i just didnt have all the information the first time  

Same gear recommendations.