You can find A440F donors from folks on this site for relatively little money. Mine was still functioning snd I gifted it to the folks in a Land Cruiser club in Connecticut (I charged them what I think any A440F is worth....$0 but Ive seen them go for $400 somewhat regularly)
If money is tight, do what
@FJ Silver said plus adjust your kickdown cable. Many times this gets them back up and rumning. It’ll always be the weak point of your rig and rebuild success has been spotty at best (hence people generally just throw in a donor or purchased used one)
The H55 swap is not technically difficult and worth your time if money isn’t as tight. The peace of mind for me made the decision easy and it changed the performance dramatically.
Try the easy stuff first, flush, fill correctly and kickdown
Check the transfer case fluid, if you pull the fill plug out and red transmission fluid comes out.....the seal between trans and xfer is leaking. When that happens your fluid level drops i. The transmission and you’ll have inconsistent pressure causing weird shifting.
I tinkered with the A440f for a couple of years. Feel free to PM if I can help you.