Re: coolant disappearing, trans issues
Always difficult to help when there is no information on the specific year/model car we are dealing with.
Assuming you have a 94 or newer with the electronically controlled 4L60E, scan the PCM for codes. There are codes for the transmission, but they don't turn on the SES light, so you don't know they are there unless you scan.
For future reference, you need to add a "Signature" with basic info about your car - year, model, engine, trans and any major mods. Helps us help you.
Left click on "User CP" on the red task bar at the top of any page. Left click on "Edit Signature" in the drop down. Enter the information in the screen that appears and save it.
94 Formula A3+1: 381ci all-forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / Comp Cams custom solid roller / TH400+GearVendors OD/4.11's / Strange 12-bolt / 300-shot N2O / Spohn Suspension / 6-pt roll bar with integrated SFC's / full AutoMeter instrumentation / MoTeC M48 Pro engine management system / a few other odds 'n ends. 800HP/800LB-FT at the flywheel.