Service Engine Light Comes on and truck shifts sluggishly
 

I have a 2000 F250 with the 7.3l Powerstroke and the service engine light occassionally. When this happens the transmission shifts very sluggishly. The Ford dealer said the computer may need to be re-programmed. I was wondering if an aftermarket chip would solve the problem and get more hp and better fuel economy. If so which one should I get?