Yep.......OP has spent some $$ and has a great stump pulling high HP/Torque motor.
Great!
Problem is truck is an OLDER F250..OP has had it a LONG time.
So issue is what year F250?
Then real information about trailers etc can be posted cause it isn't about whether that big block can tow it is about can that OLD F250 tow as in : Payload capacity, GAWRs, etc.
Towing isn't about HP/Torque. It's about vehicles ability to 'carry' the pin/tongue weight and tow it also.
I have a 2007 3500 Quad Cab auto/4:10 with 5.9L CTD that only has 325HP/610T
and tows a 14K 5th wheel........which is more trailer then your F250 can tow.
See it isn't HP/Torque.
So OP.....
What year F250?
What Cab configuration?
What tranny/rear end?
Basically what truck do you have?
Post that info and get better responses.....OK