It's not a black and white/binary answer. What's safe is a function of speed, load, ambient temperature, tire compound, etc. As
@TeCKis300 notes, get an IR thermometer and check the tire temp a few times. The FSM says you'll get a TPMS temperature DTC code at 119C/246F, so definitely stay below that.
If it helps you sleep better, the TPMS light in your truck won't come on until you're I believe 20% below the set pressure (someone please correct me if that number is wrong, I can't find the actual value in the FSM). So if you normally run 40psi you won't get an alert until you're at 32psi. Thus one could infer that the manufacturer thinks that variance is acceptable.
I'll run 5-10 miles aired down with speeds up to 40 or so without concerns. If I was driving 30-40 miles I'd spend 10-15 minutes and air up, or at least add 10psi or so. If your portable compressor can't add 10psi to a tire in 2 minutes, get a better one. 5511