[Little]

I would think this is a 'sort of' normal occurrence. Getting coolant up to temp and working an engine normally are not the same. The heads would be much hotter while pulling with exhaust temps near 1000. Also 900 rpm won't provide the oil splash that 2000+ will. If that were my engine I wouldn't be real concerned.. I would suggest taking the coach out on the highway and making the engine pull, getting exhaust temps over 900 degrees, rather than just 'operating temp'. YMMV. Good luck