It's probably not time for Texas to panic, because they still have a 5 game lead in the AL West and have managed to go 5-8 in July despite being last in OPS and runs scored. It's probably just an aberration, a blip over a mere 13 games.
This problem does not extend into late June, as they finished June on a 5 game winning streak (averaging a robust 7.6 runs per game in the process). Part of the problem may be that they've played 9 of these 13 games on the road, and while they're the 6th best hitting (in OPS) team on the road, it is lower than at home.
On Monday, they start a 10 game homestand, but it will be against strong competition (Red Sox, White Sox, Angels). I expect them to come out of this hitting funk soon, but it is something to watch out for and would give hope to the rest of the AL if it continues.
Update: They broke out of their offensive funk tonight with 9 runs on 15 hits and 5 HR. Before they get too excited, it was off a struggling Ervin Santana (now 4-10 with a 6.00 ERA), who gave up 6 ER in only 1.2 IP. They were able to do this with minor production from the middle of their lineup, with the 3-4-5-6 hitters going 4-19 with 1 HR (Beltre).
They do have an extremely deep lineup, but they probably won't really take off again offensively until Josh Hamilton starts hitting again (.208 since the beginning of June with 7 HR). That's a pretty long slump for someone who was running away with the MVP race after the first few months, and it is hard to dismiss the issues he's had with his back. It will be interesting to see how they handle Dan Haren tomorrow, who is coming off the DL.