If your timing belt is still OEM, ill wait until its 98k-100k km mileage. Your T-belt has nothing to do with your sluggish acceleration. But at your mileage, it is best to take a peek at your belts, 2 kasi belt ng 4d56, yung main T-Belt at yung mas maliit na Balancer Belt. Pwedeng maputol din kasi yung balancer belt earlier than yung main T belt. (Replace as Necessary). If both of your belts are ok, Try to use OEM airfilter first and quality fuel filter then have your valve clearance adjusted to specs by a competent mechanic. Use quality diesel fuel...