angeljoin

Impala 2006 has 127,000 MLS, used tranny had it put in last year, warranty is now expired. My issue is I lost all gears except the reverse, the Drive slipped out before getting out of the driveway and 3rd wouldn't engage manually from the column shifter then the next day my 1st slipped out and 2nd wouldn't be engaged. either. I had the tranny pan dropped and found a broken piece to a band in the bottom of tranny oil pan, It looks like the part broken is to clamp or fasten to tighten the band. Maybe 1st gear clutch band broke " they think". If anyone has advice on how these bands, gears, and clutches work together let me know what a broken band even means. Is this repairable? hard to do? expensive? This is automatic, front wheel, 3,5 engine. all I know.
I would appreciate any advice at this point. Thank you!!