Determine the optimal cruise control options
JavaScript (ES6), 91 84 75 bytes

Saved 4 bytes thanks to @Neil

f=(s,d)=&gt;s-d?(q=s+10-s%10)&gt;d?s&gt;d?0+f(s-(s%10||10),d):1+f(s+1,d):2+f(q,d):""


Uses 0 for D, 1 for T, and 2 for U.