Yep.. I battled the same thing.. I started dropping weight & getting really lean, but was getting "too thin" gaunty looking & just over all thinner than I wanted to be..
Reality is, your body may be more balanced now than ever, & you're carrying your bodies "genetically" desired body weight.. I've noticed the primal diet does realign the balance your body is meant to feel & look..
However, @ 6'3" & only 160 lbs, I'm thinking you may be a little slimmer than your genetic..
Do you have very thin bones? Thin ankles, small wrist, thinner neck?
Also, did you mention how old you are?
Being able to pile up 234lbs in the 1st place leads me to think you aren't complete & totally ectomorphic.. You can put on weight if you need to.. I know you want lean muscle, not fat, but if your body can hold 234lbs, your body can probably hold some weight & bones can support it..
The key is calories.. You won't lose weight if you eat more calories than you burn.. flat out plain & simple, cut & dry.. Burn less than you take in, your going to at least stay the same & slowly gain.. Burn more than eat, you're probably going to lose weight.. No way around it.. Adding weight requires perserving some energy everyday.. (eating more calories, & burning less) Like adding bricks to a house.. Need the materials for the growth
Here's how I stopped the weight loss, & put 10-15lbs back on, while keeping my bodyfat down & staying primal..
-Lift heavy weights.. Lift to get stronger & stick to compound moves..
-Take your time between sets.. I usually rest 3-5 minutes between sets.. remember, the goal is to get stronger & build muscle, not necessarily burn fat @ this time
-Eat.. I eat 6 whole eggs for breakfast cooked in a lot of olive oil, whole avocado, banana, & quite a bit of yogurt.. That alone is over 1k in a meal.. I love 1lb steaks, I even take olive oil shots sometime through the day.. I think Fat is the key.. Eating a lot of those good fats is great for keeping calories up & not "puffing & bloating" your body up from all the carbohydrates.. Also, dairy.. Eat the sugar free, full fat yogurt.. Its been Great for me..
-The Carb Refeed is a good idea, on days you lift.. I really eat whatever the hell I want.. Non-primal foods, pizza, ice cream, etc.. I eat around 20-25 meals a week.. If I eat trashy, high calorie, whatever the hell food I want in 3 of those meals, I'm not going to get fat (& its kind of a reward).. plus the extra calories assist in supporting a calorie surplus @ weeks end..
-I personally do no cardio.. I think you're doing too much running (assuming you want to gain weight, & not lose as you said) My low carb diet leans me out.. Cardio just confuses my body.. Just my experience.. I really don't even sprint.. If I were to start sprinting or doing some cardio, I could cut my body fat in weeks to 5%, but I don't really want that look.. I currently sit around 8-9% all year & muscles stay full & rounded out (more of a masculine look & feel for the body I want).. easy to sustain also
-I make sure I sleep really good, & nap if I'm tired.. I own my own business & don't have kids (yet), so if I feel sleep deprived, I'll knock out an hour nap or so during the day.. I HAVE to get good sleep @ night to look & feel good though, & retain muscle.. Without good sleep, your body isn't going to hold lean muscle, & digestive system won't retain nutrients..
lastly, don't be afraid to take some time off from the gym.. I personally feel most people are overtrained.. If you are radically losing weight, your body may need to rest & "calm down".. The furnace is burning too hot! (A problem most people would like to have, but you have the opposite problem)
Just my experience, & things that have helped me.. I hear where you're at though, & hope this helps..
Also, dont' worry about the people saying "you're too skinny".. Most people are "too fat".. If your body fat is relatively low, you feel healthy, & you're progressively getting stronger in the gym, you're doing the right thing..
I truly believe this primal lifestyle is good & healthy for our bodies.. It took me a year for my body to somewhat adapt & balance out.. But once you get "dialed in" & hit the sweet spot where you have complete control over your body, you'll be able to add weight, lose weight, keep the same weight, add muscle, drop some unwanted muscle (may feel too bulky), etc easily.. Its pretty cool when you get to that spot but keep doing what you're doing & you'll get there