Ahowell,
Is there another dealer you can take it into and have it inspected? My old man has the same truck as you and it pulls better than my previous 2006 F150 5.4 with tow package etc. While I do agree a 3/4-ton will defiantly give more room to spare I'm not seeing anything saying that your truck should not be able to do it.
If it was me I would find another dealer / shop and have it inspected. Explain to them what happened and see if they can identify anything, if not take it for a short trip on the highway and see how it does. These 1/2-ton's are a different breed compared to what they used too. My first truck I owned was a 2001 F150 7700 Series, which is just a 2000 F250 Light Duty. Now they have 7200lb base model, 7700 Max Tow, and 8200 Max Tow / Max Payload version's.
I wouldn't just give up on the truck if your husband enjoy's it, it might be worth the 200 bucks to get it inspected by an independent shop. Also this forum is notorious for saying anything other than a flat bed trailer must be towed by a 3/4-ton. You may want to check out f150online.net and post on their forum as they are specific to these trucks, someone might be able to tell you what to look for rather than a new truck.