If it's in decent shape, the manufacturer limits are fine...but as mentioned, the actual curb weights for the truck are not on the sticker, so a quick run thru the scales wouldn't be a bad idea.
Do make sure to include passenger weights and other cargo weight both in the truck and in the trailer. No one tows with an empty truck and empty trailer. Usually best to assume the GVWR of the trailer as a starting point.
As far as what trailer you can pull, you need to check a few criteria:
- Max Tow weight
- Max hitch weight (if using a WD hitch adjust for that).
- Max CGVWR
- Max rear axle weight rating (include verification that the tires are rated as high as the axle/suspension)
If all of those are within the limits, you are within the manufacturer limits and should be fine.
If the truck has problems/faulty systems, you should fix them and not try to de-rate the tow capability as there is no good way to do it.