Three on the tree action:
Forward from neutral position : pull toward you & down for 1st gear; lift up, push away (through neutral), and lift up for 2nd gear; straight down for 3rd gear from there.

Your issue sounds like a direct shift into 3rd gear. Lots of variables that could make that not be the case- I only mention it because you said you were new to the three on the tree action.

But... I am new to the inline sixes as well, so there is probably a better explanation.

Brad

Wrench Fetcher, PhD