Mobile home financing is tough to find let alone competitive rates for it. Have you tried community banks or credit unions? US Bank used to do them, but I'm not sure if they still do.
Your rate may not be that bad at 5.370% for a mobile home. Unlike "Stick built homes" which historically hold or increase their value, mobile homes depreciate. Once you find a lender you may find that your lack the equity you need to be approved or that the new rate would justify the expense of the refinance.
Please don't misunderstand, I'm not demeaning you or mobile homes, these are just the way the industry views them and has for a very long time.
Values do not depreciate in a resident owned community contrary to what many on this thread have told you. However, if the home you are seeking to purchase is in a rent/lease park/community you can an often do have problems with financing especially if it's a PRE HUD home. You will be putting more down and will pay a higher interest rate regardless of your credit or LTV.
MH's in rent/lease communities can depreciate as the rent increases. However, if the park/community is in a desireable area or in the path of progress you can and usually do realize some level of value and in many cases even appreciation. However, if it's a PRE HUD home it's almost impossible to see any appreaciation at all.