Can I pull a 1989 35' Jayco with my truck?
Probably not. 1/2 ton pickups are not really great at towing anything significant, and a 35' trailer is pretty significant. You can find out for sure by finding out what your GCVW for the truck - the total weight of the truck and trailer, and then subtract the curb weight (loaded for travel) of the truck from that to find out the maximum weight of the trailer. Find out the GVW of the trailer (usually on a plate on the side or a sticker inside the kitchen cabinet and you should know right away if it is acceptable. Even if the GVW of the trailer and the curb weight of the truck is <= the GCVW of the truck, be aware that 10 to 20 % of the trailer weight is applied to the truck as pin weight, and this often exceeds the maximum rear axel weight of many 1/2 ton trucks.
Exceeding any of the truck weight limits may seem to work, but you could find yourself being dragged backwards down a hill, or worse, rolling down a hill, spending a lot of time with the truck in the shop, or really scary, having an accident and facing a horde of ravenous lawyers.