Replace or repair 1998 Chevy Z71 auto transmission 1st and Rev only

Help, I need advice. My 1998 Chevy Z71 4x4 has had 2 trannie rebuilds and now is broke again. Only have 1st and reverse. I think this is a 4L60E transmission. Should I try to have it rebuilt again, or buy a rebuilt or used trannie?
Is there an aftermarket or heavy duty replacement option?
In other words, this model transmission seems to have inherent breakdown problems and can I put a different transmission in there?
I found a used trannie for $750 or I can buy a rebuilt one for $1350.
Is it possible to convert to a manual trannie?

I love my truck, it has never got me stuck. Engine is still strong and uses no oil. Needs some body work and interior is trashed but it is paid for and been in my family for 11 years. I really want to keep it and fix it up for my son, but, I can't continue to spend money to fix this dang trannie every other year.

Frustrated in Mobile Alabama. I hope someone can help me solve this dilemma.

Thanks  

I'M CURIOUS IF ANYONE EVER GAVE YOU ANY ADVICE ON THIS MATTER. MY SON'S TRANI IN HIS 98 Z71 HAS *** THE BED AND I HEAR A REBUILD IS ONLY A TEMPORARY FIX. WHAT DID YOU DO? I JUST PUT A BRAND NEW SET OF HEADS AND A $400 RADIATOR IN IT & I'M TRYING TO DECIDE WHICH ROUTE TO GO ON TRANI. HE'S 22 AND HE LOVES THE TRUCK AND CAN'T AFFORD ANOTHER ONE, PLEASE ADVISE IF YOU CAN!  

look for a 4l80e trans its a heavy duty trans bolts in 4l60e is a problem child obviously..i have 2 trucks a 94 silverado 2500 series with the 4l80 in it have no issues and takes lots of abuse.. my other is a 96 tahoe...with the 4l60e trans.. both are exelent drivers  
drive it like ya stole it...\m/