This is probably the biggest downfall of using the 1UZ engine for an engine swap for a race car or off-road vehicle. The timing belt has been known to skip a tooth on the cams during hard use. The 4.0L Lexus 1UZ engine wasn't meant for abuse in front of a manual transmission. Timing belts are known to skip a tooth from the harsh on and off throttle transitions in mud and playing around on the street. I don't think this is a problem for off-road use in general but when traction is at it's highest then there is a lot more stress on the "long-throw" timing belt. This usually happens in super sticky mud and on the street with grippy tires. Usually off-road the traction isn't that great and there is a lot of wheel spin so it's not stressful. But when you add a whole lot of traction the belts are under much more stress and tend to slip under higher loads.
I've personally thrown my belt off a tooth during an insane burnout, pedal-to-the-floor throttle while popping the clutch. Then the other week I was simply doing some high rpm accelerating because it's a shame not to run these engines above 7,000 rpm every now and then.
I think this led to a timing belt slip on the 1UZ because while I was driving later on I noticed something wasn't right. I drove it home and decided to investigate at another time. Sure enough it was the dreaded belt slip. I think this was because of a failing after market tensioner that I installed brand new when I built the engine. ONLY USE STOCK OEM TIMING BELT TENSIONERS
on Lexus/ Toyota engines. That is if you are going to use your engine under higher loads than normal.