One of the things I hated about my old first gen. I eventually did the 700r4 conversion on mine and never had another issue (until I broke the torque converter playing in the mud). Another item to keep an eye on is the governor. Pull the vacuum line off it every time you are under there dropping the fluid and check to see if there is any fluid in the line. If there is any sign of fluid change out the governor.
Your explorer is really close to how I wanted to build my old one. Unfortunately I drove it into the ground before I had the money to build it. Today I look back and regret ever parting it out.