If a dealer did it, there may be a sticker on the front of the engine specifying the mileage when done. You really can't tell by eyeballing the belt--they usually don't show obvious wear. If you're familiar with working on vehicles, you could do it yourself, but it IS a vital repair, so it's certainly safer with someone who's trained to do them. If you determine it does need it, make sure you also change the water pump--it's buried under all the same stuff, behind the timing belt, so it doesn't make sense to do the labor twice (the part isn't terribly expensive, but the labor to replace it is the same as a timing belt). Your truck really IS beautiful--it looks like it just came off the showroom floor!