Not to make "light of your situation" but let's look at what you posted:
We have a 2017 Keystone Cougar (That year model was introduced in 2016. The 2024 models are on dealer lots, so your trailer is potentially an eight year old trailer. What date did you buy it and was it new or used?)
and have problems with the slideouts since we purchased it. (What have you, the dealer and Keystone done during the previous 8 years to fix/maintain the slide? Could you explain the kind of problems you've had and the history of repairs that were done?)
We now have a really bad problem so that we can't even use one of the large slideouts.(what really bad problem? Could you describe what the problem is)
We were told that it would be $7,500 to fix. (who told you it would cost that amount? What troubleshooting/diagnostics did they do to arrive that that recommendation)
Keystone won't help us at all because it's over a year old and not in warranty. (Why would you think an eight year old problem should be covered by an expired one year warranty, 7 years after the warranty expired? Have you tried to get Ford or GM to fix an 8 year old vehicle that is out of warranty for free, or even help with partial payment? )
Our purchased warranty won't cover it either. (Please explain that warranty. Do you mean a "dealership forever warranty" or did you buy an "aftermarket extended warranty/service policy" ? Most provide coverage for 3 or 5 years, so is it still valid or has it also expired? What does the "small print" in that warranty exclude?)
We found out that Keystone was using the wrong type of slide mechanism, something that was faulty. ( What do you mean, "the wrong type of slide" There were hundreds/thousands of trailers of that model manufactured since 2017, why is this not a major topic being discussed if "all those trailers were built with incorrect slide mechanisms? This is the first I've heard of such a major issue as the "wrong type of slide" )
They won't take responsibility for this and say we are on our own in handling it. (again, why do you believe that this is Keystone's responsibility on an 8 year old trailer? What are the "circumstances that would cause Keystone to be responsible?)
Customer service was very rude and said the matter was closed and not to bother contacting them again.
I'll end with this comment: While I'm sorry that you are having issues with your trailer, the fact remains that it is LONG out of warranty. You've not stated whether you are the original purchaser, whether you are the second or even the third or subsequent owner. You've given only some basic comments with none of the "circumstances that affect/influence the problem, what has been done to fix it in the past and why you were led to believe that the slide is "the wrong mechanism". You've not mentioned any "dealer recommendations, dealer involvement in reporting the problem to Keystone nor have you told us what Keystone said was the reason for their refusal to accept responsibility.
I hope you get a good outcome from this problem, but if you're wanting any help or suggestions from the forum, much more information will be a tremendous help in arriving at suggestions or ways to move forward.
Good Luck with this issue, with more info, maybe someone can offer you a better alternative than you've been offered so far.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS