Are you talking for a diesel?? If gas, then why talk about Rotella as that is a diesel engine oil? If there is any build-up whatsoever within any engine, you are so far from using a good oil, it is not worth having a conversation....
Mobil 1 should not be used in a diesel.
Mobil makes two oils suitable for a diesel. Mobil Delvac 1 and Mobil Turbo Diesel Truck 5W-40. AFAWK, they are both the same fluid in different bottles. It is probably the best diesel engine oil on the market.
However, the differences in performance between those oils and Shell Rotella T 5W-40 will be small.