Hydro-locked engine

Hydro-lock question on a 2004 Ford Ranger 4.0L with 30,000 miles on it(yes 30,000 but it runs like it has 80,000+). Yesterday I was taking my truck through some puddles and when I got to one that was too larger for my truck I hit the bottom of the puddle and the engine stalled along with all of my electronics. I got it towed to my mechanic. I took all of the spark plugs out and what my mechanic said was that the started actually jammed the engine so it couldnt turnover. He took out the starter and fixed it and put it back in but then turned the engine over by hand. All of the water came out and my mechanic said the rods or anything wasnt broken. So here comes my question. When I installed the my new spark plugs back in and changed the oil acouple times I drove my truck around for awhile. At first it was fine to drive and it idle perfectly. I get home after about 15 minutes of driving and I put it in park (aside from the new grinding noise I hear after putting it in park). It starts idling funny as in it idles at about 1k rpm then goes down to about 700 rpm then back up. Im wondering if its because I put the spark plugs in wrong or if I damaged one of the connectors while taking them on/off. What could that possibly be? Please just dont tell me its the engine haha.