I thought the PGRE is only offered in April, October, and November, so if you aren't doing it in April (too soon anyways), then you will have a lot of time to be studying.
I think the best resource to gauge the level of knowledge required is to do the old exams. The 2008 exam (which you can find on the ETS website and they will send it to you if you register) is very very similar to the Oct and Nov 2011 exams so I imagine this is the direction things are heading too.
I noticed that the 2011 exam, compared to the 2009 exam and practice exams from before that, has a lot less computation/calculations. For example, in older exams, sometimes you were given the half-life of some particle (eg. muon) and told that it is moving relativistically so that an observer in the lab frame sees it move some length before decaying and you are asked to find the speed. So, you had to basically had to solve for both the lifetime and velocity of the particle. This involved algebra where you have something like beta/sqrt(1-beta^2) factors, and you could either grind it out, or use a taylor expansion to simplify the denominator etc.
This is a bit more difficult than the question I received in the 2011 exam where we were instead giving the lifetime of the particle as seen in the lab frame. Now, you just apply the time dilation equation and solve for beta.
So, the concept tested is the same, except the newer questions appear to be much less algebraically involved so that it's more reasonable to finish them in the time limits.
As for your course background, what you have is good, except for your modern physics -- it might be helpful to study the equivalent of a "modern physics" course, especially to get the usual ~half-semester of special relativity.
QM2 is not very useful for PGRE (I don't remember any of it at all actually). Griffiths is the perfect review material for QM1 on PGRE. The only computations you really do are expectation values or probabilities. You should know qualitatively how the wave function of a particle looks in free space, when it hits a potential barrier, and in the standard potentials reviewed by Griffiths.
Stat Thermodynamics / Stat Mech is often seen as ~3 questions on the test where you should know how to use the partition function, and how to write a partition function for an ensemble. It might not be worth learning, but if you do, just learn the partition function!
For "laboratory methods", there are two types: Error analysis and "history". For error analysis, make sure you understand Poisson errors and standard deviations. You could be asked something like "how many observations needed to get an error level less than X%" or given a series of measurements and asked to find the error on the best estimate of the value. For history questions, it's either you know the experiment they are talking about, or you don't.
It's okay to not have the 4th year level courses because a lot of students who write the PGRE are actually doing in April of their 3rd year or Fall of their 4th year!