First, Ford touted the F150 a cpl yrs back as having a 3000# load capacity!
(Bullchit advertising I know, have an 08, 05 before that and it won't carry a sick monkey's breakfast on the factory springs!
I have helper springs (which are starting to sack out now after continuous use for 5 years and 2 trucks) and carry an 88gal fuel tank and big Weahterguard box stuffed to teh gills (no winter traction pronlems! haha). Truck drives fine, but lots more weight xferrd to the front axle, had to get camber adjusted a couple times to keep front tires on it.
That said, 50k miles and I drive snowy roads every day.
I've seen waaay bigger piles o crap trucks driving around Michigan, rusted out ready to drop a wheel or sumthing and the police aren't waiting around the corner to bust them.
These days everyone thinks you need to have a 1ton dually diesel to pull a go kart trailer or load a bale of hay in the bed! I have a big diesel which drives and pulls nicer than the F150, but the F150 gets it done. SLow down a bit, take the corners easier, you'll be fine. You drive truck for a living, so you know how to drive, you know about top heavy loads. Run what you got.
Overload springs will help a ton. For the best ride/handling, get a set of airbags that adjust pressure side to side based on load. You'l give about $500 for a setup like that versus maybe $200 for a nice set of overloads, but then it'll corner real nice.
If you really want to stiffen up the susp (not necessary IMO for only several sled trips a year), get a set of aftermarket front struts.
You got what? 1200lbs of sleds (unless they're Yamis, haha) and another 500lbs of sled deck. No way you cant haul 1700lbs on a F150.