What am I doing

Hi everyone my first post. I have a 2002 Chevy 2500HD 3/4 ton 4.10 gears that pulls our 4,000lb (fully loaded) 18' expandable trailer like a dream. On all but the steepest grades I'm able to keep around 65mph without redlining the engine. I can accelerate up to speed on on ramps with ease I really don't feel that trailer back there at all.

We are just about to purchase a 6,500lb(fully loaded)25'toy hauler, how bad is this going to kill my performance. I don't want to be flooring this truck just to get 45mph on a grade that with my other trailer I had no problems. Is the extra 3,000 pounds going to have a huge impact on my 3/4 ton??? The toy hauler at 25' is still claiming to be 1/2 ton towable.

Any help will be greatly appreciated