Feeling a drop in serum testosterone at the end of the week isn't at all uncommon and that is why SWALE prescribes hCG near the end of the week to help fill that gap as hCG stimulates the leydig cells to produce testosterone and add some testosterone as the testosterone cypionate begins to drop. However, it sounds like you are experiencing the drop a bit earlier.
It is really hard to know what is happening without labwork. Maybe your dose of testosterone cypionate dosage is insufficient. Also, I know that you have been sensitive to estradiol issues. Estradiol tends to peak a little bit later than when testosterone peaks, so I think it is possible that your estradiol is in fact too high.
It makes sense that stable hormone levels are more difficult to maintain with weekly dosing as opposed to daily dosing of a compound gel or cream.
SWALE never commented on it and probably sees no reason for it, but we did have a discussion about twice weekly injections on the old board at http://www.sculptedbyiron.com/forum/showthread.php?t=11942
Personally, I don't notice a day to day difference like so many other guys on TRT. I have to judge my reaction to TRT on more of a monthly basis.