I have really hard shift from parking to reverse mode. what can be the reason for that? is it something major?

Hello From what I’ve seen when it comes to transmissions is take it to a dealer to have it looked at. Independent garages may tell you they can fix anything while they might just not have the knowhow… the ones who do have the knowhow are usually not easy to find nor are they cheap in comparison. Best bet is take it to a dealer as I doubt you’ll find such a solution on the internet. A big thing to consider when taking advice on the web is that the guy fixing the car usually isn’t the guy typing the words on a website…. Sorry if this isn’t a fix to your problem. Have your cheque book ready when at the dealers. Also consider that a proper fix may at the end be cheaper than multiple quick fixes... especially when it comes to the mechanics of gearboxes.

First, make sure there is no "loose change" in and around the shift lever components....its amazing what a penny will do in the wrong place.

You mean the shift lever action from P to R is real difficult? Or do you mean when the transmission engages Reverse, its engagement is really hard? Two separate issues. If it's the lever's action itself, it will likely just be in the automatic shift linkage, but I doubt that's what you mean here. Also you should know that if you are parking on an incline UP-HILL, if you do not use your parking brake, you WILL get a very hard Reverse engagement because the vehicle will rock backwards when you release the brake and bind up the Park pawl. If this is only happening in your driveway....when you stop the vehicle, apply the parking brake after putting the vehicle in Park but BEFORE releasing the foot brake. This will keep it off of the pawl. Now if that is not your problem, the first thing you need to check on a hard reverse engagement by the transmission is engine rpms. Is your engine idling below 1,000 rpms (typically 600-800rpm) and no Check Engine Light? If the rpms are high, it will make the engagement harsh but that's indicative of an ENGINE issue, not a transmission issue *necessarily*. If that's okay, then you likely have a problem with the transmission's valvebody or the transmission computer (the TCM). An automatic transmission's valvebody is an intricate assembly filled with many fluid passages, springs, valves, and check-balls. Incorrect transmission fluid, transmission additives, a clogged transmission pan filter, or buildup inside the valvebody itself can cause erratic gear engagement. Normally I would suggest a complete transmission fluid exchange and fill with genuine Ford Mercon V fluid, which is what your Lincoln should take, along with a filter and pan gasket replacement....but this isn't a guarantee, more of a "first step" approach to eliminate the basics, but it is still advisable UNLESS: you have had transmission slippage before or the fluid is dark and has a "burnt toast" smell. Anything beyond this, we're really going to need a transmission specialist to chime in.