Last week I went out and played in the snow with my truck for about 30 minutes or so, nothing too heavy, just cruising around. Ever since then, my engine feels like it's lugging in every gear and I'm burning close to 3/4 tank every 2 days or so. I thought that the rear e-brake might be partially engaged and while working under the truck today I noticed that the tailpipe is sootier than normal, which I know can be indicative of some fuel mix problems. I don't think that I have a caliper engaged or something like that because I haven't noticed any abnormal smells. Any ideas on where to start diagnosing this problem?