Does any over-the-range microwave have a powerful exhaust fan so it can handle steam, etc. from all burners?

We have a small kitchen in our cottage and wanted to get more counter space by moving our microwave from the counter to over-the-range. The exhaust fan on our over-the-range microwave is so weak it works marginally for exhausting the back burners of our range and does nothing for the front burners. We had a repair person come out and he said our fan is working properly and added that over-the-range microwave fans "don't do a very good job". The appliance sales person told us that the exhausting capabilities in the over-the-range microwaves aren't as good as what you can get in the new over-the-range exhaust hood type units (which I can understand), but I find it hard to believe that the fan built into a new appliance isn't as good as the 20 year old vent hood that we replaced. Have any of you found an over-the-range microwave unit with a powerful exhaust fan? Is it possible to replace the motor in my current unit with a more powerful one? Thanks for any help and guidance you can provide.