Dusty star-forming galaxies at high redshift (1 < z < 3) represent the most intense star-forming regions in the universe. Key aspects to these processes are the gas heating and cooling mechanisms, and although it is well known that these galaxies are gas-rich, little is known about the gas excitation conditions. Only a few detailed radiative transfer studies have been carried out owing to a lack of multiple line detections per galaxy. Here we examine these processes in a sample of 24 strongly lensed star-forming galaxies identified by the Planck satellite (LPs) at z ∼ 1.1-3.5. We analyze 162 CO rotational transitions (ranging from Jup = 1 to 12) and 37 atomic carbon fine-structure lines ([C I]) in order to characterize the physical conditions of the gas in the sample of LPs. We simultaneously fit the CO and [C I] lines and the dust continuum emission, using two different non-LTE, radiative transfer models. The first model represents a two-component gas density, while the second assumes a turbulence-driven lognormal gas density distribution. These LPs are among the most gas-rich, IR-luminous galaxies ever observed (μL ${L}_{\mathrm{IR}(8-1000\mu {\rm{m}})}\sim {10}^{13-14.6}$ L⊙; $\langle $ μLMISM $\rangle $ = (2.7 ± 1.2) × 1012 M⊙, with μL ∼ 10-30 the average lens magnification factor). Our results suggest that the turbulent interstellar medium present in the LPs can be well characterized by a high turbulent velocity dispersion ( $\langle $ ΔVturb $\rangle $ ∼ 100 km s-1) and ratios of gas kinetic temperature to dust temperature $\langle $ Tkin/Td $\rangle $ ∼ 2.5, sustained on scales larger than a few kiloparsecs. We speculate that the average surface density of the molecular gas mass and IR luminosity, ${{\rm{\Sigma }}}_{{M}_{\mathrm{ISM}}}$ ∼ 103-4 M⊙ pc-2 and ${{\rm{\Sigma }}}_{{L}_{\mathrm{IR}}}$ ∼ 1011-12 L⊙ kpc-2, arise from both stellar mechanical feedback and a steady momentum injection from the accretion of intergalactic gas.