Fiesta Issues - Dropped Mpg, Ticking, Missing

Thought I would try here for help before taking it to the garage -

Car is a fiesta (05-08 model, 1.4L tdci)

Problem 1 - it has always got 58-65mpg depending who was driving it. After a minor incident where it clipped a wheel which was in the middle of the road, bursting a tyre (garage found nothing wrong) I changing all 4 tyres the mpg has now dropped to 54-56. The new tyres are Bridgestone turanzas, the old ones were the same but bought part worn. Thought the mpg may have been down to the new tyres, but it has now been about a month and 1500 miles and it is showing no signs of improving.

Problem 2 - there is a ticking noise when accelerating. The back box of exhaust was replaced a few months ago, although it sounds more like it is coming from the engine. Have had problems with fuel injector seals, and all 4 have been replaced within the last year. Could be this again?

Problem 3 - the car stutters, almost misses sometimes - it is always at 30mph in third when you take your foot off after accelerating, or the same at 40 in 4th. Doesn't happen every time and never at any particular time (does it when engine is hot and cold). Spoke to the garage about it when fuel injectors were done but they didn't find a problem (and it typically didn't do it when I took the mechanic out in it).

Any opinions would be appreciated - just wondered if anyone had similar issues/what the cause was.