I have a 1998 avalon xl loaded and it has a feature where it locks all doors automatically when put in drive and then unlocks them again when you go into park.
I'd rather it not do this. I haven't seen anywhere anyone even mention this... but if there's a way like holding in or doing some sequence with the power lock buttons to disable the option I'd appreciate knowing it.

The feature you're talking about is "AutoLoc" which is built into the TVIP system. You need to get the song and dance instructions for your TVIP system in order to disable this. Do you know what model TVIP you have installed?