Hauling a Deere B

It has the factory class 3 hitch with a capacity of 500 lb downpressure and 5000 lb pull. I think I should change it out to a class 5 with 1000 lb down pressure and 12000 lb pull but it is a 300 dollar expense. Some co-workers think I can get away with using the class 3 but they have no financial investment in this venture. I really don't wanna see my new B pass my new truck.

First question - Should I have any concerns about pulling the trailer with this truck on the interstate for so many miles?

Second question - Should I change out the reciever for a heavier one?

It's a nice truck but I'd rather have my grandpa back:-(

Selling the 150 isn't even an option. My family took grandpa's death a bit hard. It only took five weeks from him getting sick to him dying. When he heard he had lung and liver cancer, it was like someone flipped off a switch in him.

Anyhow, all the aunts and uncles are attaching sentimental value to all his possessions. I would get way more grief than I'm willing to take if I sell his truck in the next few years. Until then, I gotta keep it and can't afford both.

Does anyone have an idea on whether I can risk keeping the reciever I have or be safe and buy a beefier one?