Performance of parallel concatenated trellis-coded modulation (turbo TCM) with Ungerboeck type constituent codes with maximum likelihood decoding over the AWGN channel is analyzed by extending the method of performance evaluation proposed by Benedetto et al. for binary turbo codes with uniform interleaving. Although a performance evaluation of turbo TCM has been proposed, the system model discussed in the proposal has some auxiliary interleavers only necessary for the evaluation. This paper removes such auxiliaries. Since the direct extension of Benedetto's method for turbo TCM needs huge memories for computation, an efficient numerical evaluation method is proposed in order to reduce the memory requirement. Based on the analysis, the relation between bit error rate and interleaver size is discussed. The analyzed performance is compared with simulation results of iterative decoding of turbo TCM.