Larger tires change the load on your engine so that the engine cannot provide the torque needed to move the truck at various speeds. You need to change the gearing on your drivetrain to get the engine power band and driveline loading back to normal.
I put 30 inch BFG-AT/KOs on my 1.6 8-valve Samurai with a stock drivetrain. While the engine was an improvement over the 1.3, I still had power problems in daily driving. This last weekend, I swapped my 3.73 Ring and Pinions for 4.62 units and the drivability difference was amazing! No bogging down at highway speeds in 4th or 5th gear. I could let the clutch out at idle while stopped on level ground and the engine did not die or struggle.
Redlining the engine will eventually result in a blown engine - which is a lot more expensive than re-gearing your differentials...
my 2 cents...