The weight of the oil is not going to affect the HP output of your engine to any extent that you can measure.
The proper oil weight is determined by the outside temperature where you operate your car. 30 weight oil is only good for operating where the outside temperature is lower than 90F. Go to some oil manufacturer websites to see this is true.
Ford Specs lower weight oil, becuase the thinner oil, gains, a fraction of a mile per gallon. You can't even measure the saving in several tanks of gas. BUT, you will cause more wear to your engine. Ford does not care, because they can sell more gashog, higher profit SUVs and pickup trucks by getting higher MPG ratings on cars and trucks.
You may have knocked something loose (wires or vacuum lines, or cracked a hose) when you serviced your car. If I were you, I'd go back under the hood and check everthing for disconnected hoses, or wires or damage.
And how many miles are on your spark plugs? While they will function with over 50K miles, they definitely won't perform as well? When you had the plugs out, did you check the gap? Maybe you damaged a electrode when you were in there.