4.6 v-8 help needed

[bens97tbird]

My '97 t-bird is puking coolant out of the reservoir tank when it's under load (whenever you stomp on it).... it won't do it when it's sitting in park and you rev the engine. I've replaced the thermostat, reservoir tank, and the cap. I'm beginning to think the head gasket may be bad??? no normal head gasket symptoms though, except I think I smelled combustion gasses out of the coolant reservoir when I put the parking brake on and gunned the engine while in gear to make it spit up... it runs good with plenty of power, just pukes coolant. Any ideas?