The problem usually is (OEI) trying to match shallow climb gradient capability to one's perception of the terrain gradient ahead .. as a rule, it doesn't work too well at all.
To that, there was a series of accidents in the USAF where 3 O-2s (mil Skymaster with lots of heavy ancient radios) went up a canyon with a rising floor which actually rose faster than the overweight O-2 could climb in the Nevada temps. All three, IIRC, slide onto the dirt. Terrain easily seen may be impossible to avoid, except where there is a clear opening.
A HUD is very useful here as the true horizon is superimposed on the view outside. The vast difference in AEO versus OEI performance is another factor. One gets used to AEO and its stunning what happens OEI.
GF