Jumps to "n" during a long run

[HLS]

*Good Day all We have a 1974 Evinrude 15 hp tiller steer # 15r74g Runs fine, this unit has a extended shaft installed about 3 years ago.
This year is the first we have been on a lake that we were in forwared longer than 15 min. under full thottle.* The motor will jump out of drive. If we drop back to idle and reshift we are good for may 10 more min. then the same. I have drained the lower unit found a very small amount of water and no forigen material. Put in fresh oil and back to the lake same condition. Pulled the lower unit and checked gears, bearings, shift dog and linka ge. I see nothing wrong I did check end play at prop shaft before we took apart .031" also shifter rod was turned down as far as it would go. I may add you can run this all day at 1/2 thottle with no problums. Any thoughts?
Thanks for any help*** HLS

 

[Boobie]

Sounds like a bad forward gear and clutch dog or else loose or worn shift linkage.

 

[HLS]

Thanks for the input Boobie how ever I see no signs of wear on the clutch dog or on the forward gear. All the machined cuts and edges are sharp and clear of burring. Is the lower shift rod a adjusting point? I have checked the linkage up on the power head and allappears well. If any one can tell me is the shaft end play in spec's. How ever I do not see any shims to change if it is not.
HLS

 

[shawnfish]

check the shift rod connection in the exhaust housing too....did you check the cradle on the dog?