The main reason why a new truck will not shift gears is because the engine is not yet fully broken in.

Return your shift screws back to the factory stock position (if you messed with them) and continue to run your truck until you hit about the 8th or tenth tank. Then tune for performance. The engine should scream under load when (i.e when you are driving it and running with the trigger at full pull). The engine should not stall at fll trigger pull. If it blubbers (makes a sound like "Wub Wub Wub!"), it is not fully broken in yet or you have the engine running way too lean.

With a fully broken enine running at full trigger down the street, you should hear a distinct engine noise pitch change when it shifts gears. If the engine does not reach a certain RPM, the gears will not shift.