Heavy Lift X-8 Tuning Help

Building a Foxtech D130. X-8 configuration with KV85 T-Motor, 28 inch prop, Pixhawk Orange Cube, Herelink R/C. Have built with Pixhawk before but nothing this powerful.
Aircraft flies stable in pos/hold, alt/hold. Tuning still seem to lack a lot. Drops Altitude after short horizontal flight.
Could someone please take a look at data logs and give me some guidance.