I'll light my grill, let it heat up for awhile...and then put the food on it. After awhile or sometimes right away (or even before I put the food on it) one side will POOF (if I'm standing right there I will scream) and go out and then it is whooshing but it will light up right away again but the whoosh is still coming from that side..there is flame there but it's dancing around on the ceramic plate and rarely heats up well again like the side that didn't go out.
My grill is hooked up to a permanent farm size gas tank.
First thing you'll need is a freezer full of red meat and a squat oriented power program. Stella, you're such a girl!
Sounds like you've got a gas leak somewhere.

Like a bad coupling or something. The gas builds up until it goes poof with enough force to blow out the flames on the burner but the flame stays lit at the leak and gives you a whooshing sound as it burns at a single point under high pressure. Like the sound of a plumbers torch? And so you end up with crappy pressure to the burner and not a lot of heat getting produced.
The tricky part is that it sounds like you've usually got normal pressure when you first light it up, or that it's intermittent for some reason. Plumbers use a dishsoap & water mix applied to joints & couplings with a paint brush to check for leaks (bubbles make it easy to see - works well to find a leak on tyres too), but if it's got a mind of its own or needs a little heat to start up then you might not spot it with a cold inspection. I'd see if everything (grill, ceramic radiator plate, etc) can be removed, then fire it up and let it do its usual poof thing. After you have your little scream you could remove all the stuff that's blocking your view with pliers and a hotmitt, not wearing a particularly flammable outfit, (since it probably needs all that stuff in place to allow the gas to build up and create the poof) and see if you can spot a flame jetting out from a wrong spot.
When it turns out I couldn't be more wrong, the usual Getbig excuses apply: been sick, too busy with the supermodels to workout, etc.