DME software update? Reverse low rpms wants to stall when first started???????? Help!

[02BMWX5]

OK now I really need your help!

I now have $2,000 invested in my 2002 X5 3.0

I had a independent retired BMW guy work on my X5 and cannot fix it

NO codes at all and no check engine lights at all

142,000 miles on it

He replaced the following:

Air temp sensor
Oil crankcase/seperator
idle control valve
MAF
Both O 2 sensors
Power steering hoses

The issue is this:

When I first start the X5 and put it in reverse the rpm's drop to under 500 and it wants to stall and sometimes does. If I put it into nuetral quickly the rpms go back up and normal. Sometimes it does it when put in drive but rarely.

At first we thought it was due to be very cold here but now it's 65 degrees and it still does it. But once the X5 warms up about 15 minutes of idle or driving it will not do it anymore?

Again only at first starts or after it has been sitting for a while. But it drives great and no issue after taking off.

I have heard that maybe the DME software needs updated??

Any input on what I can do next as I am out of money

I have not been to the BMW dealership yet and hope to stay out but may not have a choice.

Thanks in advance