Low-end Torque Issues — Prado 2001 (3.4L V6)

My 2001 Prado with the 5VZ-FE 3.4L V6 feels very flat below 2,500 RPM in the sand. The engine has plenty of grunt at higher revs but I struggle to maintain momentum on long dune runs without building revs first. Mechanics I've asked say the engine is fine. A few things I've tried: - Fresh air filter - Cleaned the throttle body - New spark plugs Is this just a characteristic of this engine or am I missing something? Any Prado 2001 owners here who've found solutions? Wondering about a tune or different driving technique.