Alternator question

[rjn72]

I have an 87 v30 with a 454 tbi. My problem is when the truck is idleing at a stop in the yard with nothing on it does fine. I turn on the lights and put it in gear and take off down the road, still fine. I come to a stop sign, not fine anymore. The lights dim, the alt gauge drops from about 15 to about 10.5 - 11, and a belt starts squeling like crazy. I think the alternator belt. When I leave the stop sign the volts on the alternator won't come back up and the lights won't brighten up unless I stop and turn the lights off and let it run in park for about 1 - 2 minutes. I can speed up the process if I turn off the heater and radio also. The truck has 22 lights that come on when the light switch is turned on, not counting interior lights, so I know they draw quite a bit. I think it is probably an alternator that is not putting out enough, however I am not positive. Has anyone else here had a similar problem that they could have another idea or second mine if you think a bigger alternator would fix the problem. Thanks in advance for all the advice.