Drive light blinking, car suddenly stall & suddenly accelerate

Just reach workshop: mechanic says it could be gear-box as the Drive light blinking is indication of this though he's checking/reconfirming.   In our regions, mechanics are known to be dishonest, making us charge lots of expensive parts, thus any suggestions on how to verify their recommendations will be appreciated.

Certainly changing part by part to isolate is best but most mechanics here would not do that as it is a 'waste of their time' : they wud proceed to change several parts & parts that they've installed, they wouldn't want to take out/back

A few ppl faced this "drag" & then accelerate with D light flashing:
  https://repairpal.com/04-honda-accord-transmission-d-light-has-started-blinking-821
  https://www.civicforums.com/forums/36-mechanical-problems-vehicle-issues-fix-forum/289528-blinking-d-gauge-cluster-no-acceleration.html
  http://www.nairaland.com/312061/help.my-honda-crv-drive-d

Mechanic claims that diagnostics shows no sensor/solenoid problem & he recommend changing entire gearbox
or overhaul it which will cost about $2000.  Seems like the diagnostics did not show any error from the codes

I'm sourcing other workshops for used gearbox as this car has 1.5 years more to go :
our local regulation require cars to be scraped after 10 years unless a new certification
plus certificate (of about $50000) is purchased to extend its use.

This workshop doesn't have facility to do transmission flushing (ie cleaning the gearbox):
I may consider this at another place.

The mechanic showed a handheld meter that does not indicate any alert with the gearbox's sensors & he verbally said so as well.

I'll get a 2nd opinion.  This workshop don't do transmission/gearbox flushing: have changed the gearbox oil (ie transmission fluid) &
I'm still experiencing the intermittent 'drag' &  'go' though the  Drive  light flashing did not resurface since I  reignite the car (when it
was last flashing) & prior to going to the workshop.  My gut feel is the issue is still there after gear oil change as the 'drag' is there

Is it worth trying to source for a used Honda Airwave gearbox online (eg: eBay) ?

Quick look doesn't find any.

What year Honda Airwave?

It's Honda Airwave 2009 model

The handheld device he showed me was a diagnostics tool

CVT or four speed automatic gearbox?  2WD or 4WD?

Four speed auto gearbox,  2WD

Another workshop charges $2000 too for overhauling the gearbox.

A 3rd shop offers to re-check with diagnostics : he charges $1920 (1 year warranty) for overhauling
& $1500 for replacing with a used gearbox (with 1 month warranty only).

Local regulation allows my car to go another 16 more months (by which it will have to be scrapped
or pay another $50,000 to use it another 10 more years)

I called a workshop in the country to the north where the cost of things/living is much lower:  they
charge an equivalent of $1400 to overhaul the Honda gearbox or replace it with a reconditioned
gearbox.  I then checked if they have a sister workshop (or branch) in the country that I live &
voila, they have.  The sister workshop here charges $1500 for a reconditioned (which was repaired
& tested) Honda gearbox so I got it replaced with the sister workshop.  It's now smooth