I have a '79 Johnson Seahorse 115 v4 20" with low hours on a 18' bassboat. Took it to Everglades Nat'l Park for a weekend of camping and fishing. It ran fine a month before. Changed the gearcase oil shortly before the last run. The rig was loaded down with camping gear, but not exceeding capacity. It was however the most load I have ever put on that boat. Dropped it in the water and putted out of the marina and eased the throttle up. Got to about 1/3 throttle and it slipped back into neutral 
. I was determined not to let this ruin the weekend, and eased the throttle up several times to figure how high I could get before it slipped again and ran it for awhile. The situation slowly improved as I went until it was operating normally about an hour later. It ran the rest of the weekend like a champ. It only slipped again when I was loading it under power onto the trailer at nearly 3/4 throttle. Any idea what is going on or what I should do next? My budget is seriously thin and blowing over $1000 on a new lower unit will be out of the question for a long time. I am very mechanically inclined but I lack any OMC specialty tools. Advice is appreciated. Thanks in advance.
. I was determined not to let this ruin the weekend, and eased the throttle up several times to figure how high I could get before it slipped again and ran it for awhile. The situation slowly improved as I went until it was operating normally about an hour later. It ran the rest of the weekend like a champ. It only slipped again when I was loading it under power onto the trailer at nearly 3/4 throttle. Any idea what is going on or what I should do next? My budget is seriously thin and blowing over $1000 on a new lower unit will be out of the question for a long time. I am very mechanically inclined but I lack any OMC specialty tools. Advice is appreciated. Thanks in advance.