The pronoun which is a relative pronoun that introduces the relative clause 'which sometimes stalls'.A relative clause relates information about its antecedent, 'truck'.The pronoun 'which' takes the place of the noun 'truck'.The other pronoun in the sentence is our, a possessive adjective, a word that takes the place of a possessive noun.The possessive adjective 'our' describes the noun 'neighbor' as of the speaker and one or more other people.