We've had our 2014 31FK for 53 weeks. In that time we've put about 6,000 miles on it and used it 56 nights. Our longest stays were four, 8-night trips.
We have been very pleased with the Greyhawk. All of the major components have functioned without problem: fridge, furnace, inverter, converter, water pump, televisions, A/C, slide-out, oven, cooktop, grill and microwave.
We had one issue when the Bigfoot alarm sounded indicating (falsely) that the levelers were not completely up. The fix was simply to put rubber vacuum line caps over the limit switches to ensure a better fit.
The Girard tankless water heater was tricky to get used to, but we learned. I took one really cold shower when it cut out abruptly in mid-wash. Once I found the secret reset button
and learned why it cut out, all has been well since.
The Ford drivetrain has been flawless including three trips through the N.C. mountains from Raleigh, NC to Nashville, TN and back. Our gas mileage is in the 8-9 mpg range, cruising 60-62 mph. The V10 has plenty of power to pull the loaded Greyhawk through the mountains. We have not pulled a toad, though.
We did have a list of warranty items which we accumulated during our first few trips. We put it into our dealer's shop over the winter. (Jayco's two-year warranty is a great thing.) Our work list included unbundled wires dangling beneath the chassis, surface rust on several chassis frame members, lumps underneath the vinyl flooring throughout the RV, inoperative shower light, wiring wrapped around the water filter cartridge housing making it difficult to swap out the cartridge, a tear in the padded edge along the cab-over bunk, slide-out not being quite square with the RV wall, and assorted fit-and-finish blemishes. The dealer took care of everything on the list without any arguing. Having a good dealer makes a big difference in one's satisfaction level.
We like the front kitchen on the 31FK as well as it having only one slide-out. I figure two slides doubles my chances of a slide-related problem. Also, the 31FK is configured so that it is completely useable with the slide pulled in. All cabinets, doors, etc. can be opened which is nice for those evenings we make a brief overnight stop at a Walmart and do not run out the slide.
The Greyhawks drive well, too, at least better than you'd expect a large box truck to do. The JRide Plus package on ours seems to be a great benefit.
We've had no problems with the rooftop A/C keeping cool even in the hot Southern summer weather. Granted it might be different in the Southwest. We hope to get there someday.
Most of our trips are just DW and myself, but we have done two 8-day trips with two grandkids along. Even with them along we had plenty of space. The large storage compartment in the rear is great. Just watch your weight. Visit a CAT scale when fully loaded to check your axle weights.
Spend some time sitting in the various Greyhawks. Imagine cooking and eating breakfast, getting ready for bed, spending a rainy day with everyone inside, etc. Sit on the toilet with the door closed to see how much room you have. Stand in the shower with the door closed and take a pretend bath to see how it works for you. Try to picture as best you can how that floor plan works for your needs.
In short, we love our Greyhawk. Should something happen to it, we would definitely buy another Greyhawk and from the same dealer. Best of luck and I hope this helps.