This could also be caused by rear brakes not being adjusted enough. I had the same problem with my car with the "automatic" adjusting rear brakes. They didn't, which caused the front brakes to do more of the work, causing the dip you described.
I also have Monroe shocks on my car, bought at Pep Boys for under $15 each. I have the numbers at home. I got the numbers from the CAT Shop Manual. I seem to recall that the fronts were for some big American cars and the rears were for early Corvettes (or visa versa). Anyway, I noticed a couple of weeks ago, when I jacked up the car, the rear end was being held up by the shocks - that is, the shocks hit their max length before the springs did - putting a bit of a strain on the bottom mounting pegs. Doesn't seem good to me.
I do know that KYB Gas shocks has shocks that will fit the rear - I think they were suggesting the ones for a Suzuki Sameri. However, they did not have any for the fronts that would compress as small as the original ones. I probably have those notes somewhere too, if someone wanted to follow up on them. I was worried that the suspension would bottom out on the shocks rather than the rubber snubbers. The prices on KYB's are extremely good, especially compared to other performance gas shocks.
Jay