Transmission Slipping

You mentioned engine running at 175 degs. The 175 deg seems a bit high if a carb’d engine which should have a 143 t-stat. I wouldn’t expect over 160 after hard run.   Not sure when fuel injection started but 175 would be ok as FI runs 165 t-stats.   Possibly you have a cooling problem?

Just a thought,... could your trans oil cooler be clogged? My 1980 SN had similar symptoms and I discovered a crimped oiler cooler from the previous owner. Someone had over tightened the bracket holding the cooler and compromised the cooler as a result. In addition my control cable was severely out of adjustment due to worn cable fitting. I ended up replacing the 5" cooler with a 9" one, new fluid, new cable, and rebuilt the controller. mine is much better but still not perfect yet. Some fine tuning is required.

PS. I noticed new borg warner transmissions require new trans coolers or the warrantee is voided... (skidum fine print).

Good luck Shane and keep at it !!!      

Shane,
Use dexron/mercon ATF. NO "fancy" stuff and NO synthetics. I hope it does it.

I don’t know the history of the boat but it has not overheated in the two years I’ve had it.   And both times I went out the engine temperature was running right at 175

D0es it go into reverse?   

Likely it needs to come out. Not the end of the world, these are very simple mechanisms and easy to fix.

Check the fluid level and make sure its on the high side but it don't look good -