Plane 3.2.1 firmware on APM 2.6 Issue

Just received my APM 2.6, running Mission Planner (current version) and trying to do an initial set-up. The "wizard" loads the most current version of Plane, assume 3.2.1, and then confirms the load OK. It then fails to connect to the APM via MAVLINK and won't continue with the set-up. I can load both Rover and Copter firmware (copter tells me my APM is too small for current version and loads a previous version) but the MAVLINK works fine and I have successfully finished configuring the APM in those modes. I do not have a copter, nor a rover that I want the APM in. I need the Plane version to work. First off, is there a way to tell the wizard to load an earlier version of the plane firmware? Secondly, if not, is there an earlier version of MP available that takes away the wizard to allow me to choose which version of the firmware I want to load? Third, don't know the issues with the current plane firmware, but it obviously is not talking to my autopilot, are there others out there who are having similar issues.
Thank you

This is using MP 1.3.28

Start by reproducing the report with Mission Planner 1.3.28, Plane 3.2.1, and an APM 2.6, comparing the Plane upload and MAVLink connection with the working Rover and Copter paths. The issue names no files or tests; done would mean identifying the failure's scope and providing a verified fix or a documented compatibility result.

Written by the indexing model from the issue text.