98 Supra saltare trans engagement issues

I finally got my Supra in the water for the first time this past weekend and all went fairly well with the exception of the transmission. When I bought the boat the trans was pulled and needed to be rebuilt. We got all the parts together and got the whole thing reassembled with the manual from skidim and some help from a local mechanic. On land everything seemed fine so we finally got it in the water.

We backed it down in the water and let out the winch a bit and put it in gear with some throttle to make sure it worked under load and it did so we launched it. At first everything was fine but after about 10 minutes I went to neutral and when I went back into drive it didnt engage right away, I had to throttle it up before it jerked into gear. It also started slipping after that before it stopped engaging in drive all together, reverse still worked fine.

We found out that the oil being too high can cause it to slip so we drained about a half quart out of it so it was correct on the stick. (manual says its capacity is 2 quarts but that was high on the dipstick) afterwards we noticed it engaged into drive much faster and smoother so we again put it in the water. It was again fine at first but within a minute of launching it we noticed it wasnt engaging without being on throttle a bit. Its no longer slipping though and can handle full throttle pulls with ease but the longer it runs, the more trouble it has getting into drive.

Once back on land we checked the oil, its fine. I removed the heat exchanger and trans cooler hoses. Both are free of trash and flowing nicely. What could possibly be going on here? Im at a loss as to where I should look next.