1998 Ram 1500 Burning Smell

Recently my dodge has a strong burning smell (smells kind of like rubber). It's hard to tell where it's coming from. It seems to be under the cab and close to the rear passenger side wheel most of the time. I need to make a 500 kilometer trip with the truck very soon (Thanksgiving) and I'd like to get this sorted out in case if it is potentially serious.

As a side note here is a bit of history. My truck almost redlined after it was left at idle when the heatercore blew. Upon getting it replaced the truck drove fine for a few months. Lately it takes a few more cranks to get started on moist days, seems to be a noticeable drop in power (no way to actually prove that it's not me being paranoid about the truck though) and around 90 km/h it's developed a small shimmy that you can only really feel through speed corners.

Any ideas or thoughts would be useful.