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In my past experience of aliitle to much oil. If anything happens you might get alittle leak from the front or rear seal but it will quit after awhille or you just might not have anything happen at all. 3/4 of a quart is not really much
3/4 of a quart is usually not enough to worry about. 2 or more quarts get progressively worse. as the oil level rises it will have a tendency to foam, which means that there will be air in the oil and less lubrication, this can damage engine components. You may also get oil blowout from the filler or dipstick and breathers. If you get really crazy, you will burn oil and smoke a lot. In worst cases you will get a lot of oil in the cylinders and the engine will be prone to damage during the compression stroke. Oil doesn't really compress, but engine components will, bad news.
I have never seen damage from hydraulic damage from oil in the cylinders but have heard about it a few places. I have personally put in double the oil and seen the engine smoke and run crappy, thankfully that was a lawnmower.
Don't worry about a quart or less, especially in a truck engine. On a small engine with say 3-4 quart capacity, a quart is more of a problem.
I suspect, if anything, the extra 3/4-quart may be beneficial since oil helps cool your engine. By 3/4-quart do you mean the book says 6 quarts with filter change and you put in 6&3/4 quarts (and where then is it on the dipstick?) or did you just put the 6 in and it shows about 3/4 too high on the stick?
too much oil will lock up an engine. the pistons can't go back down corectly, and force oil up into cylinders . at this point you get hydrostatic lock. i have seen this on several front wheel drive vehicles where owners have let out transmission fluid thinking it is engine drain. then add 4-5 qts. oops!
3/4 of quart should not be an issue.
On most 96-present Ford Trucks that I have dealt with (I usually dealt with about 20 a day!), the oil capacity limit, 6 quarts, shows up about half-way on the dipstick. I was taught to never fill a 96-present Ford to the FULL indicator line on the dipstick.