Stihl 026 Pro stalling?

My Stihl 026 Pro which I purchased new from a Stihl dealer has always stalled when operated tipped down after running a short while. Two returns to service department have failed to correct the problem. It starts only after 5 pulls when cold (not good), but otherwise it cuts and runs well.. I use only Stihl 2 cycle oil and regular gas. The stalling is associated with tipping the saw down (to cut up firewood after cutting tree). It acts like the flexible, rubber fuel line in the tank may be crimping or emerging from the fuel when the saw is tipped because to start the saw after it shuts itself off, I need to choke it each time. I am impressed with the recoil starter (ha) but would really like to turn this birthday present into a joy and not a frustration/danger.