Having trouble warming my muscles up

So this is going to sound weird, but I have trouble warming my muscles up sometimes. I do a warm up set and blood flows into the muscle, but instead of feeling warm and stronger and getting a pump, I get a pump but the muscle just feels tighter and weaker, even though I work up a sweat. I use pretty light warm ups, and 2 sets for bigger lifts.

It also usually corresponds to how much energy I have, ie I feel fine for the first exercise or two but anything after that I have trouble with.

My main lifts are still going up, but I feel like my accessory lifts are suffering because of this. I've put a good bit of mass on my legs and chest (enough that I look like I work out even through a shirt), but arms, shoulders, and back haven't even made strength increases.

If it matters I'm 6'0", 20, 175 lbs, and I have high blood pressure (genetic, I do cardio twice a week and can run a 6 min mile, low sodium diet etc). Also, I've been eating 2 bananas a day, so I doubt it's a potassium deficiency.

Anyone else get this?