I have a Cuisinart electric pressure cooker, and I used their recipe for Beef Brisket 2 LB., and it turned out perfectly cooked and I was able to pull it with two forks easily. 2 LB beef brisket. 1 & 1/2 cups liquid. 55 minutes on high pressure, then natural pressure release. It was juicy, tender and delicious. I did the same thing with a larger 4 LB bone-in pork shoulder roast, and it turned out the same - tender, juicy and delicious, and pullable with forks. Generally, i agree with others here that the smallest recommended amount of liquid is best, and it makes a difference whether you use natural or quick pressure release. Generally, for most meats, you want to use natural.
By the way, the instruction booklet for my cooker says to use 1 cup liquid if cooking your dish for 45 minutes or less, and 1 and 1/2 cups liquid if cooking longer than 45 minutes. Also, just as with regular cooking, when you cook meat, it is important to rest the meat for some period of time (usually tented with foil) before cutting into it. If you cut the meat without resting it while it is still extremely hot, all the juices tend to run out on your cutting board - leaving the meat dry. You generally want to let it rest at least 15-20 minutes before cutting, and longer for larger cuts. And,remember to cut your meat against the grain to help with tenderness if you aren't shredding/pulling it. Good luck!
Finally, cook times for pressure cooking start after pressure has been fully built. So, it will take some time for the pressure to build, then your cook time, followed by the time it takes for pressure to release. So, your dish will actually be cooking longer than just the cook time. If you are counting your cook time from the time you close the lid to the time you open the lid, you may actually be under-cooking.
Update from 2/15/2016: I just did a beef chuck pot roast for the first time in my pressure cooker. 3 & 1/4 LB. chuck roast. I cut it in two pieces and seasoned and browned each on all sides. Added 1 & 1/2 cups golden lager beer as the liquid. Set the machine for 80 minutes cook time, and used natural pressure release. When done, I took it out and tented it with foil and let rest 15 minutes. It was moist and falling apart tender. I pulled the meat with forks and put back in the cooking juices to store and used the meat for sandwiches. Delicious!
Update from 2/17/2016: I made another beef chuck roast similarly to the one a couple days ago. 3 & 1/4 LB. beef chuck pot roast. Cut into 3 pieces to fit in cooker. Seasoned all sides with salt, pepper and grill seasoning, and then browned all sides. Put meat back in cooker. I added 1 pkg. dry Italian salad dressing mix + 1 pkg. dry ranch dressing mix + 1 pkg. dry beef gravy mix (these three ingredients I got from another recipe online somewhere). Sprinkle all the dry mixes all over the beef. I added one whole onion cut in fourths, 2 bay leaves, 1 can cream of mushroom soup (right on top of beef), 1 can cream of celery soup (also on top of beef), and slightly less than 1 cup golden lager beer in bottom of pot. The soup plus the beer made plenty of liquid to get to the 1 & 1/2 cups. Set on high pressure, and set cook time at 80 minutes, and did natural pressure release. Let meat rest tented with foil for 15 minutes, and it was falling apart tender and juicy. I shredded it and put back in the juices to store - which by the way on their own made a great gravy! Be careful not to over salt the beef. All of the packaged dry mixes as well as the soups have some salt in them.
NOTE: I do find that with pressure cooking with a somewhat fatty cut of meat, the fat and connective tissue does not really completely break down and render into juices as it does with slow braising in the oven for several hours. So, I did have to deal with more manual fat removal with the pressure cooker method.