DLP TV is much darker lately, please help with problem

Question

Hello everyone, I found this forum after some searching around, I figure it's the best place since it is Toshiba itself, rather than a forum with all TV's.  I'm very sorry for the long message, but I wanted to share everything so that you have all the info.  I know it's hard to read through all that but I hope someone with know-how does and helps me.
My TV:  Toshiba 62" DLP (62HM84) connected through HD cables of high quality (RGB), not HDMI (I found the former is better on this TV for some reason, maybe due to the latter being new at that time)
I bought this TV within months of its release, so I've had it for a very long time, and have experience with its functions as well as how it's supposed to look like, and of course how much life to expect from the lamp/ballast.
The first lamp lasted almost 2 years, and I replaced it.  Since then I replaced the lamp on average about every year and a half (acceptable, perfectly, as the TV is on all the time).
So, after about 4 lamp replacements, it exploded again.  This time the new lamp would not work, and I found out it was the ballast.  $300 later, it was on again and working fine. 
Since this last replacement, which was well over 2 years ago now, closer to 3 years, by far the longest of any before, it's still going, minus the darkness problem, described below.
In the last few months I have noticed the TV is noticeably darker, at all times.  It was never very bright in daylight, but now it's almost impossible to watch in the day, and at night, when usually everyone who came over told us that our TV is by far the most beautiful as far as picture goes of all they have seen (even compared to new 1080p LEDs and plasmas, I guess they just don't know how to set them up properly), at night it is just nice now, no longer bright and beautiful, but just nice.  Still looks great in HD, but for some reason it's just dark. 
Contrast, brightness, HUE, Color, everything is set perfectly, I tried film/movie/video modes, LOW/HIGH (it's always on high now), and nothing.  It's still very nice, but dark, much darker then ever before, even if still very sharp and colorful.  When connected through HDMI and my laptop, it's almost unwatchable, the dark scenes are so dark you can't see anything, but I don't think that is related because on HD channels the problem is not that bad, it's dark, but watchable, and dark scenes are still normal, just not like they should be.
I am just wondering basically if this problem is an old lamp problem, which is what I'm hoping.  I can't see it being the color wheel, the colors are great and my searches brought up no such hits.  But I can't wrap my head around a bulb losing brightness over time, I always figured it's either working or not, over its lifetime, it's the reason why I chose DLP over Plasma/LCD (at the time, my next will be a LED for sure, maybe Toshiba, have to do research)
Any info would be greatly appreciated.
Thank you.
PS.  How important is it to buy an OEM lamp rather than one that is made by a third party?  I don't even know which I have now, or if Toshiba even still makes these, or if they ever did (the color wheel is Samsung, I don't think Toshiba makes any parts at all, only puts them together, but I don't know for sure, and I've always had Toshiba tv's in the past, so I'm sticking to what I know, but that may change).  When I buy the lamp, I just go by the code on the lamp, I forget it now (TB25-LMP , I think)
I just did a search for lamps, and it seems there are big differences in prices, from $72 on newegg, to $150 from some Japanese named company which claims the lamp is extremely high quality. 
If it is the lamp, I mean my problem, I want to get the best possible, if it makes a difference, the make of the lamp I mean.  Please, any help.
I'm very sorry for the long message.

Answer 1

did changing the lamp resolve your problem with the picture being dim?